I am a new Mac user. It is necessary to install an antivirus?

Not unless you’re running Windows on the computer or frequently exchange files with people running WIndows.

Viruses aren’t the only type of malware. Keep Mac OS X up to date and use common sense to protect yourself from other threats.

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No, it isn't, but see this:

Helpful Links Regarding Malware Problems

If you are having an immediate problem with ads popping up see The Safe Mac » Adware Removal Guide and AdwareMedic.

Open Safari, select Preferences from the Safari menu. Click on Extensions icon in the toolbar. Disable all Extensions. If this stops your problem, then re-enable them one by one until the problem returns. Now remove that extension as it is causing the problem.

The following comes from user stevejobsfan0123. I have made minor changes to adapt to this presentation.

Fix Some Browser Pop-ups That Take Over Safari.

Common pop-ups include a message saying the government has seized your computer and you must pay to have it released (often called "Moneypak"), or a phony message saying that your computer has been infected, and you need to call a tech support number (sometimes claiming to be Apple) to get it resolved. First, understand that these pop-ups are not caused by a virus and your computer has not been affected. This "hijack" is limited to your web browser. Also understand that these messages are scams, so do not pay any money, call the listed number, or provide any personal information. This article will outline the solution to dismiss the pop-up.

Quit Safari

Usually, these pop-ups will not go away by either clicking "OK" or "Cancel." Furthermore, several menus in the menu bar may become disabled and show in gray, including the option to quit Safari. You will likely have to force quit Safari. To do this, press Command + option + esc, select Safari, and press Force Quit.

Relaunch Safari

If you relaunch Safari, the page will reopen. To prevent this from happening, hold down the 'Shift' key while opening Safari. This will prevent windows from the last time Safari was running from reopening.

This will not work in all cases. The shift key must be held at the right time, and in some cases, even if done correctly, the window reappears. In these circumstances, after force quitting Safari, turn off Wi-Fi or disconnect Ethernet, depending on how you connect to the Internet. Then relaunch Safari normally. It will try to reload the malicious webpage, but without a connection, it won't be able to. Navigate away from that page by entering a different URL, i.e. www.apple.com, and trying to load it. Now you can reconnect to the Internet, and the page you entered will appear rather than the malicious one.

An excellent link to read is Tom Reed's Mac Malware Guide.

Also, visit The XLab FAQs and read Detecting and avoiding malware and spyware.

See these Apple articles:

Mac OS X Snow Leopard and malware detection

OS X Lion- Protect your Mac from malware

OS X Mountain Lion- Protect your Mac from malware

OS X Mavericks- Protect your Mac from malware

About file quarantine in OS X

If you require anti-virus protection Thomas Reed recommends using ClamXAV. (Thank you to Thomas Reed for this recommendation.)

From user Joe Bailey comes this equally useful advice:

The facts are:

1. There is no anti-malware software that can detect 100% of the malware out there.

2. There is no anti-malware that can detect everything targeting the Mac.

3. The very best way to prevent the most attacks is for you as the user to be aware that

the most successful malware attacks rely on very sophisticated social engineering

techniques preying on human avarice, ****, and fear.

4. Internet popups saying the FBI, NSA, Microsoft, your ISP has detected malware on

your computer is intended to entice you to install their malware thinking it is a

protection against malware.

5. Some of the anti-malware products on the market are worse than the malware

from which they purport to protect you.

6. Be cautious where you go on the internet.

7. Only download anything from sites you know are safe.

8. Avoid links you receive in email, always be suspicious even if you get something

you think is from a friend, but you were not expecting.

9. If there is any question in your mind, then assume it is malware.

Mac users often ask whether they should install "anti-virus" software. The answer usually given on ASC is "no." The answer is right, but it may give the wrong impression that there is no threat from what are loosely called "viruses." There is a threat, and you need to educate yourself about it.

1. This is a comment on what you should—and should not—do to protect yourself from malicious software ("malware") that circulates on the Internet and gets onto a computer as an unintended consequence of the user's actions. It does not apply to software, such as keystroke loggers, that may be installed deliberately by an intruder who has hands-on access to the computer, or who has been able to take control of it remotely. That threat is in a different category, and there's no easy way to defend against it.

The comment is long because the issue is complex. The key points are in sections 5, 6, and 10.

OS X now implements three layers of built-in protection specifically against malware, not counting runtime protections such as execute disable, sandboxing, system library randomization, and address space layout randomization that may also guard against other kinds of exploits.

2. All versions of OS X since 10.6.7 have been able to detect known Mac malware in downloaded files, and to block insecure web plugins. This feature is transparent to the user. Internally Apple calls it "XProtect."

The malware recognition database used by XProtect is automatically updated; however, you shouldn't rely on it, because the attackers are always at least a day ahead of the defenders.

The following caveats apply to XProtect:

☞ It can be bypassed by some third-party networking software, such as BitTorrent clients and Java applets.

☞ It only applies to software downloaded from the network. Software installed from a CD or other media is not checked.

As new versions of OS X are released, it's not clear whether Apple will indefinitely continue to maintain the XProtect database of older versions such as 10.6. The security of obsolete system versions may eventually be degraded. Security updates to the code of obsolete systems will stop being released at some point, and that may leave them open to other kinds of attack besides malware.

3. Starting with OS X 10.7.5, there has been a second layer of built-in malware protection, designated "Gatekeeper" by Apple. By default, applications and Installer packages downloaded from the network will only run if they're digitally signed by a developer with a certificate issued by Apple. Software certified in this way hasn't necessarily been tested by Apple, but you can be reasonably sure that it hasn't been modified by anyone other than the developer. His identity is known to Apple, so he could be held legally responsible if he distributed malware. That may not mean much if the developer lives in a country with a weak legal system (see below.)

Gatekeeper doesn't depend on a database of known malware. It has, however, the same limitations as XProtect, and in addition the following:

☞ It can easily be disabled or overridden by the user.

☞ A malware attacker could get control of a code-signing certificate under false pretenses, or could simply ignore the consequences of distributing codesigned malware.

☞ An App Store developer could find a way to bypass Apple's oversight, or the oversight could fail due to human error.

Apple has taken far too long to revoke the codesigning certificates of some known abusers, thereby diluting the value of Gatekeeper and the Developer ID program. Those lapses don't involve App Store products, however.

For the reasons given, App Store products, and—to a lesser extent—other applications recognized by Gatekeeper as signed, are safer than others, but they can't be considered absolutely safe. "Sandboxed" applications may prompt for access to private data, such as your contacts, or for access to the network. Think before granting that access. Sandbox security is based on user input. Never click through any request for authorization without thinking.

4. Starting with OS X 10.8.3, a third layer of protection has been added: a "Malware Removal Tool" (MRT). MRT runs automatically in the background when you update the OS. It checks for, and removes, malware that may have evaded the other protections via a Java exploit (see below.) MRT also runs when you install or update the Apple-supplied Java runtime (but not the Oracle runtime.) Like XProtect, MRT is effective against known threats, but not against unknown ones. It notifies you if it finds malware, but otherwise there's no user interface to MRT.

5. The built-in security features of OS X reduce the risk of malware attack, but they are not, and never will be, complete protection. Malware is a problem of human behavior, not machine behavior, and no technological fix alone is going to solve it. Trusting software to protect you will only make you more vulnerable.

The best defense is always going to be your own intelligence. With the possible exception of Java exploits, all known malware circulating on the Internet that affects a fully-updated installation of OS X 10.6 or later takes the form of so-called "Trojan horses," which can only have an effect if the victim is duped into running them. The threat therefore amounts to a battle of wits between you and Internet criminals. If you're better informed than they think you are, you'll win. That means, in practice, that you always stay within a safe harbor of computing practices. How do you know when you're leaving the safe harbor? Below are some warning signs of danger.

Software from an untrustworthy source

☞ Software with a corporate brand, such as Adobe Flash Player, doesn't come directly from the developer’s website. Do not trust an alert from any website to update Flash, or your browser, or any other software. A genuine alert that Flash is outdated and blocked is shown on this support page. Follow the instructions on the support page in that case. Otherwise, assume that the alert is fake and someone is trying to scam you into installing malware. If you see such alerts on more than one website, ask for instructions.

☞ Software of any kind is distributed via BitTorrent, or Usenet, or on a website that also distributes pirated music or movies.

☞ Rogue websites such as Softonic, Soft32, and CNET Download distribute free applications that have been packaged in a superfluous "installer."

☞ The software is advertised by means of spam or intrusive web ads. Any ad, on any site, that includes a direct link to a download should be ignored.

Software that is plainly illegal or does something illegal

☞ High-priced commercial software such as Photoshop is "cracked" or "free."

☞ An application helps you to infringe copyright, for instance by circumventing the copy protection on commercial software, or saving streamed media for reuse without permission. All "YouTube downloaders" are in this category, though not all are necessarily malicious.

Conditional or unsolicited offers from strangers

☞ A telephone caller or a web page tells you that you have a “virus” and offers to help you remove it. (Some reputable websites did legitimately warn visitors who were infected with the "DNSChanger" malware. That exception to this rule no longer applies.)

☞ A web site offers free content such as video or music, but to use it you must install a “codec,” “plug-in,” "player," "downloader," "extractor," or “certificate” that comes from that same site, or an unknown one.

☞ You win a prize in a contest you never entered.

☞ Someone on a message board such as this one is eager to help you, but only if you download an application of his choosing.

☞ A "FREE WI-FI !!!" network advertises itself in a public place such as an airport, but is not provided by the management.

☞ Anything online that you would expect to pay for is "free."

Unexpected events

☞ A file is downloaded automatically when you visit a web page, with no other action on your part. Delete any such file without opening it.

☞ You open what you think is a document and get an alert that it's "an application downloaded from the Internet." Click Cancel and delete the file. Even if you don't get the alert, you should still delete any file that isn't what you expected it to be.

☞ An application does something you don't expect, such as asking for permission to access your contacts, your location, or the Internet for no obvious reason.

☞ Software is attached to email that you didn't request, even if it comes (or seems to come) from someone you trust.

I don't say that leaving the safe harbor just once will necessarily result in disaster, but making a habit of it will weaken your defenses against malware attack. Any of the above scenarios should, at the very least, make you uncomfortable.

6. Java on the Web (not to be confused with JavaScript, to which it's not related, despite the similarity of the names) is a weak point in the security of any system. Java is, among other things, a platform for running complex applications in a web page, on the client. That was always a bad idea, and Java's developers have proven themselves incapable of implementing it without also creating a portal for malware to enter. Past Java exploits are the closest thing there has ever been to a Windows-style virus affecting OS X. Merely loading a page with malicious Java content could be harmful.

Fortunately, client-side Java on the Web is obsolete and mostly extinct. Only a few outmoded sites still use it. Try to hasten the process of extinction by avoiding those sites, if you have a choice. Forget about playing games or other non-essential uses of Java.

Java is not included in OS X 10.7 and later. Discrete Java installers are distributed by Apple and by Oracle (the developer of Java.) Don't use either one unless you need it. Most people don't. If Java is installed, disable it—not JavaScript—in your browsers.

Regardless of version, experience has shown that Java on the Web can't be trusted. If you must use a Java applet for a task on a specific site, enable Java only for that site in Safari. Never enable Java for a public website that carries third-party advertising. Use it only on well-known, login-protected, secure websites without ads. In Safari 6 or later, you'll see a padlock icon in the address bar when visiting a secure site.

Stay within the safe harbor, and you’ll be as safe from malware as you can practically be. The rest of this comment concerns what you should not do to protect yourself.

7. Never install any commercial "anti-virus" (AV) or "Internet security" products for the Mac, as they are all worse than useless. If you need to be able to detect Windows malware in your files, use one of the free security apps in the Mac App Store—nothing else.

Why shouldn't you use commercial AV products?

☞ To recognize malware, the software depends on a database of known threats, which is always at least a day out of date. This technique is a proven failure, as a major AV software vendor has admitted. Most attacks are "zero-day"—that is, previously unknown. Recognition-based AV does not defend against such attacks, and the enterprise IT industry is coming to the realization that traditional AV software is worthless.

☞ Its design is predicated on the nonexistent threat that malware may be injected at any time, anywhere in the file system. Malware is downloaded from the network; it doesn't materialize from nowhere. In order to meet that nonexistent threat, commercial AV software modifies or duplicates low-level functions of the operating system, which is a waste of resources and a common cause of instability, bugs, and poor performance.

☞ By modifying the operating system, the software may also create weaknessesthat could be exploited by malware attackers.

☞ Most importantly, a false sense of security is dangerous.

8. An AV product from the App Store, such as "ClamXav," has the same drawback as the commercial suites of being always out of date, but it does not inject low-level code into the operating system. That doesn't mean it's entirely harmless. It may report email messages that have "phishing" links in the body, or Windows malware in attachments, as infected files, and offer to delete or move them. Doing so will corrupt the Mail database. The messages should be deleted from within the Mail application.

An AV app is not needed, and cannot be relied upon, for protection against OS X malware. It's useful, if at all, only for detecting Windows malware, and even for that use it's not really effective, because new Windows malware is emerging much faster than OS X malware.

Windows malware can't harm you directly (unless, of course, you use Windows.) Just don't pass it on to anyone else. A malicious attachment in email is usually easy to recognize by the name alone. An actual example:

London Terror Moovie.avi [124 spaces] Checked By Norton Antivirus.exe

You don't need software to tell you that's a Windows trojan. Software may be able to tell you which trojan it is, but who cares? In practice, there's no reason to use recognition software unless an organizational policy requires it. Windows malware is so widespread that you should assume it's in every email attachment until proven otherwise. Nevertheless, ClamXav or a similar product from the App Store may serve a purpose if it satisfies an ill-informed network administrator who says you must run some kind of AV application. It's free and it won't handicap the system.

The ClamXav developer won't try to "upsell" you to a paid version of the product. Other developers may do that. Don't be upsold. For one thing, you should not pay to protect Windows users from the consequences of their choice of computing platform. For another, a paid upgrade from a free app will probably have all the disadvantages mentioned in section 7.

9. It seems to be a common belief that the built-in Application Firewall acts as a barrier to infection, or prevents malware from functioning. It does neither. It blocks inbound connections to certain network services you're running, such as file sharing. It's disabled by default and you should leave it that way if you're behind a router on a private home or office network. Activate it only when you're on an untrusted network, for instance a public Wi-Fi hotspot, where you don't want to provide services. Disable any services you don't use in the Sharing preference pane. All are disabled by default.

10. As a Mac user, you don't have to live in fear that your computer may be infected every time you install software, read email, or visit a web page. But neither can you assume that you will always be safe from exploitation, no matter what you do. Navigating the Internet is like walking the streets of a big city. It can be as safe or as dangerous as you choose to make it. The greatest harm done by security software is precisely its selling point: it makes people feel safe. They may then feel safe enough to take risks from which the software doesn't protect them. Nothing can lessen the need for safe computing practices.

There will always be threats to your information security associated with using any Internet - connected communications tool:

1. You can mitigate those threats by following commonsense practices
2. Delegating that responsibility to software is an ineffective defense
3. Assuming that any product will protect you from those threats is a hazardous attitude that is likely to result in neglecting point #1 above.

The answer to your specific question "It is necessary to install an antivirus?" is no.

OS X already includes everything it needs to protect itself from viruses and malware. Keep it that way with software updates from Apple.

A much better question is "how should I protect my Mac":

• Never install any product that claims to "clean up", "speed up", "optimize", "boost" or "accelerate" your Mac; to "wash" it, "tune" it, or to make it "shiny". Those claims are absurd.

  Such products are very aggressively marketed. They are all scams.

• Never install pirated or "cracked" software, software obtained from dubious websites, or other questionable sources.
  • Illegally obtained software is almost certain to contain malware.
  • "Questionable sources" include but are not limited to spontaneously appearing web pages or popups, download hosting sites such as C net dot com, Softonic dot com, Soft pedia dot com, Download dot com, Mac Update dot com, or any other site whose revenue is primarily derived from junk product advertisements.
  • If you need to install software that isn't available from the Mac App Store, obtain it only from legitimate sources authorized by the software's developer.
• Don’t supply your password in response to a popup window requesting it, unless you know what it is and the reason your credentials are required.
• Don’t open email attachments from email addresses that you do not recognize, or click links contained in an email:
  • Most of these are scams that direct you to fraudulent sites that attempt to convince you to disclose personal information.
  • Such "phishing" attempts are the 21st century equivalent of a social exploit that has existed since the dawn of civilization. Don’t fall for it.
  • Apple will never ask you to reveal personal information in an email. If you receive an unexpected email from Apple saying your account will be closed unless you take immediate action, just ignore it. If your iCloud, iTunes, or App Store account becomes disabled for valid reasons, you will know when you try to buy something or log in to this support site, and are unable to.
• Don’t install browser extensions unless you understand their purpose. Go to the Safari menu > Preferences > Extensions. If you see any extensions that you do not recognize or understand, simply click the Uninstall button and they will be gone.
• Don’t install Java unless you are certain that you need it:
  • Java, a non-Apple product, is a potential vector for malware. If you are required to use Java, be mindful of that possibility.
  • Java can be disabled in System Preferences.
  • Despite its name JavaScript is unrelated to Java. No malware can infect your Mac through JavaScript. It’s OK to leave it enabled.
• Beware spontaneous popups: Safari menu > Preferences > Security > check "Block popup windows".
  • Popup windows are useful and required for some websites, but unsolicited popups are commonly used to deceive people into installing unwanted software they would never intentionally install.
  • Popups themselves cannot infect your Mac, but many contain resource-hungry code that will slow down Internet browsing.
  • If you ever receive a popup window indicating that your Mac is infected with some ick or that you won some prize, it is 100% fraudulent. Ignore it.
  • The same goes for a spontaneously appearing dialog insisting that you upgrade your video player right this instant. Such popups are frequently associated with sites that promise to deliver "free" movies or other copyrighted content that is not normally "free".
  • The more insistent it is that you upgrade or install something, the more likely it is to be a scam. Close the window or tab and forget it.
• Ignore hyperventilating popular media outlets that thrive by promoting fear and discord with entertainment products arrogantly presented as "news". Learn what real threats actually exist and how to arm yourself against them:
  • The most serious threat to your data security is phishing. Most of these attempts are pathetic and are easily recognized, but that hasn't stopped prominent public figures from recently succumbing to this age-old scam.
  • OS X viruses do not exist, but intentionally malicious or poorly written code, created by either nefarious or inept individuals, is nothing new.
  • Never install something without first knowing what it is, what it does, how it works, and how to get rid of it when you don’t want it any more.
  • If you elect to use "anti-virus" software, familiarize yourself with its limitations and potential to cause adverse effects, and apply the principle immediately preceding this one.
  • Most such utilities will only slow down and destabilize your Mac while they look for viruses that do not exist, conveying no benefit whatsoever - other than to make you "feel good" about security, when you should actually be exercising sound judgment, derived from accurate knowledge, based on verifiable facts.
• Do install updates from Apple as they become available. No one knows more about Macs and how to protect them than the company that builds them.

Summary: Use common sense and caution when you use your Mac, just like you would in any social context. There is no product, utility, or magic talisman that can protect you from all the evils of mankind.