Anyone have a solution for moldy kegerators?

[YamahaXS]

I had some mold growing on my kegs....Probably I didn't rinse them off well or something after filling them. Anyways, for now I have wiped them down and cleaned my kegerator, but I was curious if this is a common problem and whether or not there is a easy way of preventing this (assuming washing off the out side of the keg is insufficient).

cheers and beers
Jeff