unlikely trend scanner is used by millions of people, if you wan tto a bogus site and did it , its possible it could infect it, but if you went to their site highly unlikely.
are you running any sort of kaaza or bearshare etc, sharing apps of any kind ? most virus infections come from either that or emails.
since you aren't running either a firewall or a virus scanner, you are toast. next you be telling us you dont use windows update
note some clever virus programmers made it so that they will detect you installing a virus scanner and disable it, so if it doesnt find anything,try one from a boot disk.