ho letto circa la possibilità di un trojan...

1) controlla tra i processi:
C:\Downloads\Hijack this\HijackThis.exe


2) controlla nel registro potresti avere queste voci:

R1 - HKCU\Software\Microsoft\Internet Explorer,SearchURL = http://magicsearch.ws/?q
R1 - HKCU\Software\Microsoft\Internet Explorer\Main,Search Bar = http://magicsearch.ws/?q
R1 - HKCU\Software\Microsoft\Internet Explorer\Main,Search Page = [url]http://magicsearch.ws/?q
R0 - HKCU\Software\Microsoft\Internet Explorer\Main,Start Page = http://magicsearch.ws
R1 - HKCU\Software\Microsoft\Internet Explorer\Main,Default_Page_URL = http://magicsearch.ws
R1 - HKCU\Software\Microsoft\Internet Explorer\Main,Default_Search_URL =http://magicsearch.ws/?q=
R1 - HKCU\Software\Microsoft\Internet Explorer,Search = http://magicsearch.ws/?q