Ubisoft's website has been hacked, leading to user's account information being accessed and therefore compromised.
Ubisoft has already began a thorough investigation with relevant authorities, security experts have recommended that users change their passwords as soon as possible, as the company works on restoring the integrity of any compromised systems.
You can always change your Ubisoft password here, and, honestly, I suggest doing so now, if you can. No personal payment data is stored on the site, so debit or credit card information is safe from the breach. User names, email addresses and encrypted passwords are at risk.
Ubisoft made a full formal statement here, with information on how to safeguard your account. You should really do this immediately to avoid any hassle down the road.