Tseric from Blizzard released the following information to offer some suggestions on how to keep your WoW account safe.

Compromised Account Information

With the recent rise in reports of compromised accounts, we felt that it would be in the best interest of the community to bring this topic into the spotlight. This is an effort to educate our customers about what can be done to should your account become compromised and most importantly, what you can do to prevent it from becoming compromised.

Tips for keeping your account secure:

-Don’t share your information with friends/guild mates.
-Don’t use “leveling” services.
-Change your password often. Also, make sure that you don’t follow a pattern when you change your password (ex: 123Bob, 123Bobb, 123Bob1, 123Bob2)
-Avoid UI mods with executables since they could contain Trojans that transmit your account information back to the host.

We urge you all to review the current policy which can be found here: http://www.blizzard.com/support/wowgm/?id=agm01889p

You can check out the full thread here.