From the 0wned horses' mouth :
"We recently discovered that one of our websites was exploited to gain illegal access to some of our online systems. As a result we recommend that all Ubisoft account holders change their password here: https://secure.ubi.com/register/ForgotPwd.aspx?genomeId=5b61fa9f-305b-422b-aa3a-0efcf8370dec&lang=en-US&nexturl=http%3A%2F%2Fwww.uplay.com. Please note that no personal payment information is stored with Ubisoft so your credit/debit card information was safe from this intrusion.
Full details of the incident can be found here: http://ubi.li/5zwub. We would like to sincerely apologize for any inconvenience this may cause and thank you for your understanding."