Google Product Forums
Re: Youtube account compromised!!!
PeggyK Jun 14, 2012 10:17 AM
Posted in group: YouTube
Unfortunately I don't think there is any way to completely shut off the ability to move the YouTube account to a different Google account, since that ability is only an option for a  fraction of existing YouTube accounts. 

Have you signed out of all sessions in your YouTube account? Then changed your password and added Google account recovery options?  You might also want to set up 2 step verification: http://support.google.com/accounts/bin/answer.py?hl=en&answer=180744