If your site is forwarding to another site that contains a virus and you did not make any changes to your site, then you maybe a victim of SQL injection, if your site uses SQL.
See http://en.wikipedia.org/wiki/SQL_injection
For examples on SQL see http://unixwiz.net/techtips/sql-injection.html
Email any time or call 01480 26 00 00 014 80 26 00 00