You're surfing along, Facebooking or emailing or building a new playlist for your iPod. Suddenly, a window pops up telling you your computer is infected, but this product can clean it for you. The pop-up looks legitimate, like AVG or other another antivirus program, or even Windows. You think "yes, please do clean my computer" and click the link to start. Oops. You've just opened the front door for the trojans.
Rogue antivirus and security programs like Security Tool are popping up again. Where and how we get them is a lengthy explanation. The thing to remember is, it's usually one of the last things you clicked on.
If this happens to you, stop what you're doing immediately and reboot the computer into Safe Mode (usually pressing F8 on and off during startup will do it). Then try a System Restore to a previous date before the infection. Then run CCleaner and the free Malwarebytes; remove all found. Subsequent scans with SUPERAntiSpyware, SpyBot and a few other good scanners may clean it out. If not, give me a call.