Hi Michael,
It looks like your website has been compromised. "Normally" this virus code copies itself in all index.php pages but again depending on code type, it could be any file.
@WPyogi gave a great list of links to get website cleaned. But if you are not pro, my humble honest opinion will be to get professional help.
Edit:
http://sitecheck.sucuri.net/scanner/ is a great tool, it'll tell you exact files which are infected after you perform a scan, you may remove infected code from the files then.