The One About Trojan Horse

A friend of mine asked me how come his PC has trojan horse right
not, as he doesn't download files and do harmful things to his PC.

I told him that sharing USB drive, open connection ( 24 hours broad
band connection ), surfing prawn photos, hackers and all sorts of
reason contributed to Trojan horses etc.

Him, " Then ? How do I get rid of these Trojan Horses ? "

Me, " Simple, you put in 2 hungry tigers and 2 hungry lions, and
in no time the horses and cows and sheep would be all gone !! "

My friend -__-" and har ???