Trojan's getting through

[Draco86]

Malware can  really screw with ones computer
I tend to use Malwarebytes and Super Anti Spyware both free
update them then deleat Any restore points (because viruses hide there and can not be removed by avast)
start in safe mode scan computer with those two programs then run a boot time scan

That never fails for me, but it will take a long time

[EntitY]

No single AV will detect or prevent all malware from getting on a system. That is why you should use other security scanners periodically. Sometimes it's a persistent browser-hijacker and usually malware will hide in System Restore. Malwarebytes, SuperAntiSpyware, and A-squared are what I use as scanners every two weeks or so. I would use a 3rd party browser instead of IE, because most malware is targeting IE.  You might also look into learning about and using, Sandboxie, Returnil and Disk-Imaging.