Windows Defender is getting high marks and good reviews. Gina had some persistent infections on your Gateway computer, and I spent several hours tracking down individual trojan removal instructions and tools unsuccessfully trying to clean it up. I was preparing to wipe the hard drive and reinstall the operating system (again). Then I tried Defender (download here), and its detection and removal process seemed to do the trick. Her computer has been operating OK without the constant distruptive trojan detections from her AV.