I'm not sure about Bitcoin being "untraceable, and very easy to hide," since Bitcoins take the form of a public ledger, so they're actually more traceable than cash. In theory you can thwart it by using a mixing service (you deposit into the service along with many others, then withdraw the same value but not the same coins), yet there's stories like this that suggest an aggrieved party (say someone who had coins stolen from them), can trace the money by sending micropayments that effectively tag it. (The Bitcoin equivalent of "slightly irradiated bills"). Each transaction in the ledger is also recorded and publicly viewable for all time, so even if the software for tracing transactions and matching them to real entities doesn't yet exist, the data will wait until it is.