The FBI has issued a warning about the growing number of attacks using Facebook, after an alarming increase in the use of hacked accounts to trick people out of money, typically by mailing 'friends' with requests for cash after a claimed robbery.

The agency's Internet Crime Complaint Center has detected over 3,200 such attacks since it started monitoring, and the numbers are rising sharply. Some people are losing thousands of dollars as they attempt to help friends in need.

Facebook has said that it is aware of the problem and is trying to find technical fixes. The firm is also working with third parties to minimise the effectiveness of such attacks.

"On the technical side, we have improved a number of our automated systems to better handle this unique class of scam, and are taking efforts to ensure that we adapt our response to the scam as it changes," Facebook said in a blog posting.

"At the same time, our security team is working with law enforcement and collaborating with email providers and other industry experts to identify and catch the criminals responsible. Western Union is also working closely with law enforcement on scams such as this one."

Malware writers are increasingly using hacked accounts to harvest data, distribute malware and direct users to phishing sites, the FBI warned. Once a PC is infected it can compromise the business or home network of which it is a part.

"Cyber thieves are also using spam to promote phishing sites, claiming a violation of the terms of service agreement or creating some other issue which needs to be resolved," the FBI said.

"Other spam entices users to download an application or view a video. Some of these messages appear to be sent from friends, giving the perception of legitimacy. Once the user responds to a phishing site, downloads an application, or clicks on a video link, the electronic device they're using becomes infected. "

The FBI advises users to lock down privacy settings, limit friends and report any instances of hijacking immediately.