trojan horse removal

im running avast pro 4.8 on windows7 ultimate.
im having a problem with the following trojan: JSFakeAV-DB[trj]
the web scanner finds it and says it has done away with it before it has entered my computer, but it is not correct , the trojan has installed itself and causes errors on ie8 and redirects google search. the only way i could get rid of it was to do a system restore. running a full and thorough scan does not find it either. what is wrong. please help thanks,steve stv357.

http://www.sophos.com/security/analyses/viruses-and-spyware/trojfakeavdb.html some info on this. i believe malwarebytes anti malware removes this TROJAN/FAKEAV and its variants http://www.malwarebytes.org/malwarenet.php?name=Trojan.FakeAV download this freeware here, http://download.cnet.com/Malwarebytes-Anti-Malware/3000-8022_4-10804572.html?part=dl-10804572&subj=dl&tag=button