Upgrade to SSD??

An SSD simply means you have a faster disk drive for booting, opening, and storing files. It will not make the computer any faster. Only a new computer with a faster processor can do that. But your sense of performance is enhanced because an SSD handles disk-based data faster.

The best thing for you to do is get rid of any malware on the computer and uninstall any anti-malware software you have installed. Download and run EtreCheck 2.0.11. Copy the output and paste in your next message here. Then I can better address your questions.

Helpful Links Regarding Malware Problems

If you are having an immediate problem with ads popping up see The Safe Mac » Adware Removal Guide, AdwareMedic, or Remove unwanted adware that displays pop-up ads and graphics on your Mac - Apple Support.

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.

A lot of the time, the causes of performance drops on computers doesn't really have anything to do with the hardware, and has everything to do with the software you have installed. There's no doubt that an SSD would speed up your Mac, but is it necessary? Probably not. I'd bet there's some junk software you need to remove, and that will solve the problem.

First, as Kappy recommended, download EtreCheck, run it and post the report here. That will give us a better idea of what you've got going on.

Then, see my Adware Removal Guide for help removing Genieo, and any other adware that may be installed.

If, after we've helped you get your Mac cleaned up, the performance still isn't where you want it to be, an SSD may be a good investment. I can honestly say that the difference in performance, specifically related to reading from and writing to the hard drive, I saw when I bought a new Mac with an SSD was astonishing. But, at the same time, dumping an expensive SSD into a six-year-old Mac may not be the best way to spend the money, either.

(Fair disclosure: I may receive compensation from links to my sites, TheSafeMac.com and AdwareMedic.com, in the form of buttons allowing for donations. Donations are not required to use my site or software.)

Okay, looks like one probable cause of the issue is Sophos. Uninstall that, using the uninstaller that Sophos places in your Applications folder (called Sophos Remove or Remove Sophos).

Another issue is that you only have 2 GB of RAM, which is bare minimum for Yosemite, and your system is definitely running low on RAM in your report. Removing Sophos may help, but if you're going to run a modern system on that hardware, low RAM is going to be a chronic issue. You could upgrade your RAM - and that's probably a higher priority than changing the hard drive - but again, you'll be dumping money into an old system, and that may not be the best investment. Still, RAM is pretty cheap these days, so we're not talking about the same level of expense as adding an SSD.