There are about 400 million facebook users (or with a login that is)
Of those the biggest list untill now was being put up for sale on the net by a Russian hacker at giveaway prices. The list claimed to have about 1.5 million logins.
According to sources already 700.000 of those have effectively been sold.
Time to change your password of Facebook
Even if the chance is one in 400
It is just good security.