do i need security software for imac?

No you will be fine

If you feel nervous, you can download ClamXav to make sure that any viruses that come to you through emails from Windows machines will be caught.

Under no circumstances install Norton, it is incompatible with Apple OS X.

You may find the following information useful:

VIRUSES

No viruses that can attack OS X have so far been detected 'in the wild', i.e. in anything other than laboratory conditions.

It is possible, however, to pass on a Windows virus to another Windows user, for example through an email attachment. To prevent this all you need is the free anti-virus utility ClamXav, which you can download for Tiger and Leopard from:

http://www.clamxav.com/

The new version for Snow Leopard is available here:

http://www.clamxav.com/index.php?page=v2beta

Note: ClamAV adds a new user group to your Mac. That makes it a little more difficult to remove than some apps. You’ll find an uninstaller link in ClamXav’s FAQ page online.

If you are already using ClamXav: please ensure that you have installed all recent Apple Security Updates and that your version of ClamXav is the latest available.

Do not install Norton Anti-Virus on a Mac as it can seriously damage your operating system. Norton Anti-Virus is not compatible with Apple OS X.

FAKE ANTI-VIRUS SOFTWARE and associated MALWARE

Do not be tricked by 'scareware' that tempts computer users to download fake anti-virus software that may itself be malware.

Fake anti-virus software that infect PCs with malicious code are a growing threat, according to a study by Google. Its analysis of 240m web pages over 13 months showed that fake anti-virus programs accounted for 15% of all malicious software.

Scammers trick people into downloading programs by convincing them that their PC is infected with a virus.

Once installed, the software may steal data or force people to make a payment to register the fake product.

Beware of PDF files from unknown sources. A security firm announced that by its counting, malicious Reader documents made up 80% of all exploits at the end of 2009.:

http://www.computerworld.com/s/article/9157438/in which Rogue_PDFs_account_for_80_of_all_exploits_says_researcher

TROJANS and RE-DIRECTION TO FAKE WEBSITES

The appearance of Trojans and other malware that [i]can[/i] possibly infect a Mac seems to be growing, but is a completely different issue to viruses.

If you allow a Trojan to be installed, the user's DNS records can be modified, redirecting incoming internet traffic through the attacker's servers, where it can be hijacked and injected with malicious websites and pornographic advertisements. The trojan also installs a watchdog process that ensures the victim's (that's you!) DNS records stay modified on a minute-by-minute basis.

You can read more about how, for example, the OSX/DNSChanger Trojan works (by falsely suggesting extra codecs are required for Quicktime) here:

http://www.f-secure.com/v-descs/trojan_osx_dnschanger.shtml

SecureMac has introduced a free Trojan Detection Tool for Mac OS X. It's available here:

http://macscan.securemac.com/

First update the MacScan malware definitions before scanning. You can also contact their support team for any additional support - macsec@securemac.com

The DNSChanger Removal Tool detects and removes spyware targeting Mac OS X and allows users to check to see if the trojan has been installed on their computer; if it has, the software helps to identify and remove the offending file. After a system reboot, the users' DNS records will be repaired.

(Note that a 30 day trial version of MacScan can be downloaded free of charge from:

http://macscan.securemac.com/buy/

and this can perform a complete scan of your entire hard disk. After 30 days free trial the cost is $29.99. The full version permits you to scan selected files and folders only, as well as the entire hard disk. It will detect (and delete if you ask it to) all 'tracker cookies' that switch you to web sites you did not want to go to.)

A white paper was published on the subject of Trojans by SubRosaSoft, available here:

http://www.macforensicslab.com/ProductsAndServices/index.php?main_page=document_ general_info&cPath=11&products_id=174

Also,beware of MacSweeper and MacDefender (also goes under the name of MacProtector, MacGaurd, MacSecurity or MacShield):

These are malware that misleads users by exaggerating reports about spyware, adware or viruses on their computer.

You can keep up to date, particularly about malware present in some downloadable pirated software, at the Securemac site:

http://www.securemac.com/

HOW TO AVOID RE-DIRECTION

Adding Open DNS codes to your Network Preferences, should give good results in terms of added security as well as speed-up:

[b]If you are using a single computer:[/b] Open System Preferences/Network. Double click on your connection type, or select it in the drop-down menu, and in the box marked 'DNS Servers' add the following two numbers:

208.67.222.222

208.67.220.220

(You can also enter them if you click on Advanced and then DNS)

Sometimes reversing the order of the DNS numbers can be beneficial in cases where there is a long delay before web pages start to load, and then suddenly load at normal speed:

http://support.apple.com/kb/TS2296

There may be other ways of guarding against Trojans, viruses and general malware affecting the Mac, and alternatives will probably appear in the future. In the meantime the advice is: be careful where you go on the web and what you download!

WHAT TO DO IF YOU THINK YOUR MAC HAS BECOME 'INFECTED'

If you think you may have acquired a Trojan, and you know its name, you can also locate it via the Terminal:

http://theappleblog.com/2009/04/24/mac-botnet-how-to-ensure-you-are-not-part-of- the-problem/

Although any content that you download has the possibility of containing malicious software, practising a bit of care will generally keep you free from the consequences of anything like the DNSChanger trojan.

1. Avoid going to suspect and untrusted Web sites, especially p'orn'ography sites.

2. Check out what you are downloading. Mac OS X asks you for you administrator password to install applications for a reason! Only download media and applications from well-known and trusted Web sites. If you think you may have downloaded suspicious files, read the installer packages and make sure they are legit. If you cannot determine if the program you downloaded is infected, do a quick Internet search and see if any other users reported issues after installing a particular program.

3. Use an antivirus program like ClamXav. If you are in the habit of downloading a lot of media and other files, it may be well worth your while to run those files through this AV application.

4. Use Mac OS X's built-in Firewalls and other security features.

5. LimeWire (now defunct) and other peer-to-peer sharing applications and download torrents supplying pirated software, movies etc are hotbeds of potential software issues waiting to happen to your Mac. Everything from changing permissions to downloading trojans and other malicious software can be acquired from using these applications. Similar risks apply to using Facebook, Twitter, MySpace, YouTube and similar sites which are prone to malicious hacking: http://news.bbc.co.uk/1/hi/technology/8420233.stm

6. Resist the temptation to download pirated software. They can contain Botnet Trojans. SecureMac offer a simple and free tool for the removal of the iBotNet Trojan available here:

http://macscan.securemac.com/files/iServicesTrojanRemovalTool.dmg

YOUR PRIVACY ON THE INTERNET and the latest risks to look out for:

There is the potential for having your entire email contact list stolen for use for spamming:

http://www.nytimes.com/2009/06/20/technology/internet/20shortcuts.html?_r=1

NOTE:] Snow Leopard, OS 10.6.x, offers additional security to that of previous versions of OS X, but not to the extent that you should ignore the foregoing:

http://www.apple.com/macosx/security/

Apple's 10.6.4 operating system upgrade silently updated the malware protection built into Mac OS X to protect against a backdoor Trojan horse that can allow hackers to gain remote control over your treasured iMac or MacBook.

http://www.sophos.com/blogs/gc/g/2010/06/18/apple-secretly-updates

And if you are using iPhone Apps you are also at risk of losing all privacy:

http://www.engadget.com/2010/10/03/hacker-claims-third-party-iphone-apps-can-tra nsmit-udid-pose-se/

The advent of HTML5 may also be a future threat to internet privacy:

http://www.nytimes.com/2010/10/11/business/media/11privacy.html?_r=1&hp

Security of OS X generally:

http://www.apple.com/macosx/security/

http://www.nsa.gov/ia/_files/os/applemac/I731-007R-2007.pdf

Security Configuration for Version 10.5 Leopard:

http://images.apple.com/server/macosx/docs/Leopard_Security_Config_2nd_Ed.pdf