I ussualy use :

1. spy sweeper ( free ) -- http://www.webroot.com/wb/downloads
2. Trojan Hunter ( free ) -- http://www.antivirus-online.de/engli...nttro.php3?a=4
3. Norton System works --- Symantec site

after accessing the internet and finishing my job .

or u can visit http://www.disk-utility.com/wipe-hard-disk.html.