I got the following SMS from number 32665 (FBOOK):
"Confirmed! To edit SMS preferences go to m.facebook.com/settings. To turn off all SMS messages reply stop. Reply help for other option. SMS charges may apply"
I'm worried someone hacked into my account, since I did not do anything in the last weeks that would generate this message. I think this SMS means somebody enters a confirmation code in a new deviced to be recognized. For example, the message is generated in the following simple hack. That hack which was fixed quickly.
Is there a way I can find out why this SMS was sent? Sadly, the activity log doesn't show security-related actions (such as logins). I didn't see any unknown devices under "Security > Your Browsers and Apps", but someone could potentially delete himself after checking something out. I had login notifications & login alerts on all the time.