how the fuck did i get a trojan

I never download pirated or otherwise untrusted or suspicious software and I keep all my Windows and I don't use Internet Explorer, and I keep Firefox and Thunderbird up-to-date.

And yet my antivirus software just found a couple of trojans on my system.  How the shit did they manage their way on my system?

It supposedly cleaned them on the last scan, but I rebooted and am now re-scanning just in case these were the "lol I'm not really gone lol I'm back whenever you reboot" variety.

These things happen from time to time, just be glad your antivirus caught them.

Either you used IE, downloaded bad software, or it's a false positive. These things don't just happen.

>>3
If you are connected to the Internet, they do.

>>1
www.linux.org

I'm on a college network, and when I'm booted up in windows my antivirus shows a "blocked a trojan" notice at least every half-hour.  Seems that the network has almost as many STDs as the student population. 

>>4
No, they don't.

>>5
Sure, but you'll only get infected if you never apply security updates (ie. if you're an idiot).