Yes, it is easier to counterfeit bank notes. It is easier to counterfeit 2 bank notes and use them on the flee market.
No, it is not easier to steal significantly many users without getting caught.
Worms that do all kind of things are daily business in the Windows world today. If such a worm sends all the money of wallets it finds to the thief's wallet, there is no way to charge back or find the thief.
Above mentioned counterfeiter would even risk to get caught on the flee market. The BTC thief has almost no risk at all for a good chance to make millions.
Still I think that such worms are not a threat to BTC as a whole as people would call that bad luck for those not locking their wallets away or using other precautions.