According to the infographic blog post of Facebook they said about 600,000 log-ins per day are compromised. That's given some the false impression that there are that many accounts compromised every day.
While Facebook does block (approximately) 600,000 log-ins per day, it is not that these Facebook accounts are compromised on Facebook, and certainly not that they're 'hacked' as some have written. There may be compromised accounts that appear on Facebook, but more often than not they are compromised off of Facebook--they use the same password for e-mail as Facebook, they get phished, etc. Compromised in this sense refers to log-ins where we are not absolutely confident that the account's true owner is accessing the account and we either preemptively or retroactively block access.
For more information and to download the Facebook security infographic Click Here