Spybot will detect only some, very dangerous viruses, your Anti-virus should pick up trojans and Zonealarm will stop them.
I dont know of any good FREE trojan scanners only the cleaner from moosoft is good but you do have to pay. I can honestly say, Moosoft's software has never found one as I keep everything very much like you up-to-date.
Look at click here
This anti-virus grabs trojans but is not out yet.
So I am sure you are safe.