Hi riya: In addition to The Cleaner as MsMittens mentioned, I use Trojan Defence Suite (aka TDS). You'll find it here http://www.diamondcs.com.au/tds/

I have found it to be a very good trojan hunter and a little more stable (Cleaner tends to jam on large file systems or lots of files) and more thorough. I do use both as best practices dictate.

Regards.