The vBulletin team recently announced that they suffered a compromise which allowed the attackers access to vbulletin.com servers and database. On their own words:
We take your security and privacy very seriously. Very recently, our security team discovered sophisticated attacks on our network, involving the illegal access of forum user information, possibly including your password. Our investigation currently indicates that the attackers accessed customer IDs and encrypted passwords on our systems. We have taken the precaution of resetting your account password. We apologize for any inconvenience this has caused but felt that it was necessary to help protect you and your account.