It is reported that thousands of Bangalore based Facebook accounts hacked and links to their morphed pornographic pictures are sent to those who in their friend list.
Facebook says the hackers used dome browser vulnerability to hack the accounts of the victims
Facebook said in a statement that this happened because of some Java script error in some browsers and that the hackers would have used that error to intrude into Facebook. The other speculation, according to experts, is that some apps might have gone rogue. "Once permissions are given to the app, it continues to use it unless specified otherwise
If you think your account is hacked
1. Change password, a strong password is always better.
2. Remove third party apps (Privacy Settings => Apps and websites => Remove unwanted or spammy apps.)
3. Scan your computer with a good anti-virus.
and please check this link to know what Facebook tell you to do.