Congrats Marsha_Mallow on finding and getting rid of the maleware/virus on your machine.
And Thank you for the very good explanation of Windows vs Linux/Unix OS file permissions, je_saist
I'm a network engineer and I use Microsoft Security Essentials / Malwarebytes on my Windows machines. I don't care much for ratings or #'s from magazines or other professionals, I prefer to use what I deem to be effective (and in this case, free).
...And geez je saist, know much about network security? 
I'd like to throw in my $0.02 on this subject (I'm a network manager/programmer/DB admin/all-around IT guy).
-ClamWIN - great program, but a little "wonky" in the user-interface, as je_saist mentioned.
-WinPatrol - This is not an anti-virus program, but it is very helpful in its own right. Its main function is that it monitors all of the startup locations in your PC, and asks you to authorize any programs that are registered in those areas. So if something tries to register itself to start when Windows starts, WinPatrol will catch it and allow you to deny it if you want. It also allows you to monitor your services and configure them, and monitors IE addons as well. The paid version has additional capabilities, such as HijackThis log generation, Killbox, and showing hidden files. Invaluable in combating a malware infestation. Oh, and the paid version is $30, and you can install it on every computer you own for that one $30 payment. http://www.winpatrol.com/
- NoScript - this is an addon for FireFox/SeaMonkey. What it does is what the name says: it blocks ALL scripts on web pages you visit. Flash scripts, Javascript, PDFs...none will run unless you allow them.
- FlashBlock - another FireFox/SeaMonkey addon. Blocks Flash. Nice second layer of defense behind NoScript.
- AdBlock Plus - yet another FireFox/SeaMonkey addon. This blocks ads on websites. Many "safe" websites may still be showing you infected ads, and that's where you get hit. Block the ads and cut off one more vector for infection. And as a bonus, your web browsing should be a bit faster as well, since you aren't downloading ads on every site.
These things won't make you 100% infection free, but I know for a fact that having them has saved me many infections in the past.
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