[cypher]

How long have you had him? It's quite common for young Russian hams to do this especially if they have got used to being hand fed treats. Most grow out of it with a little time & realise that fingers aren't food!
If this happens I generally stop hand feeding for a while, if they begin to nibble I just gently remove my hand or if I'm holding them put them back into the cage, still offer treats but just lay them down in front of your ham, if you do this for a few days to a week you should begin to notice a change.

Just wanted to add that if you didn't get your ham from a breeder (I know there aren't that many in the US) he will be a hybrid not a WW so you will need to take a bit more care with diet if that is the case as they can be prone to diabetes, avoid anything sweet, fruit, treats with honey or sugar etc.