reddgone

Hypothetically speaking lets say I downloaded some software from one of those hip sharing sites such as firewire. The software I downloaded was scanned with all the proper anti virus programs and it came back clean. Is it possible that their still could be some sort of Trojan horse embedded in a file somewhere? If their was how would I know? or how could I find it?

P.S. please don't waste my time with the illegal mambo jumbo, just answer the question as I asked it if you know. Thank You.