Chanserv doesn't take over channels. Chanserv has nothing to do with nicks. If somehow someone else has taken control of them (eg: changed the password, etc), then the options are:
1] you picked passwords that were very easy to guess
2] you shared your passwords
3] you used a script that sent your passwords to someone else
The chance that someone actually hacked into the database to steal your passwords is negligibly small. I don't know what network you're on, but most networks I know of consider password security a user's responsibility, and opers will not return nicks that were lost due to reasons 1] 2] and 3].