One of the questions I get more than anything is, "How do I avoid getting a virus"? There are actually a few things you can do to avoid getting a virus.
The number one thing is getting a good antivirus program. An antivirus program is a program you install on your computer. Basically, it lies dormant in the background and scans every file that goes in and comes out of your computer to see if it has a virus in it. It's really important to have a program like that installed, and to keep it updated.
You don't necessarily have to pay for a program like that, there are many good free alternatives out there that work just as well, if not better than the paid ones, but you do have to have one on at all times.
The second thing is to stay updated. Update Windows, update your browser, update your plugins. It's really important to keep the latest version of everything.
Another way to avoid viruses is to stay away from file extensions that you don't know. For example, if you go on a certain website and you're trying to download a video, and you download a file but suddenly it has an exe extension, that's not a video, that's an executable, a program. I would definitely try to avoid that kind of file.
Another tip is, if something sounds too good on the Internet, it usually is. If you see a free add for an iPod, or you just need to download this program to sign up for this great service, most of the time, they're full of it. I would try to avoid anything that looks too good.
The last thing, I would say, is try to avoid using Internet Explorer, or earlier versions of Internet Explorer. All the alternative browsers out there like, Firefox or Chrome, do a much better job at securing your computer. They're much faster, and have a lot more features.