i want to add that it's more of a incompetence of the average user, that don't know how to protct their wallet, many don't even run antivirus, or they download too many shit on their machine
thieves would have an harder time if people knew how to use their pc better
But if we go for the largest bitcoin losses - the inputs wallet, bitcoin savings and trust, gox, numerous dark markets - it had nothing to do with bad pc security and everything to do with being gullible and not applying due diligence.
You can have the securest computer ever, but it counts for nothing if the coins are handed over willingly by people who should know better.