Facebook's new online messaging service makes users of the social networking site more vulnerable to identity theft by cybercriminals, computer security firm Sophos warned Thursday.
It urged users to be aware of the security risks before signing up for Facebook's next-generation online messaging service that blends online chat, text messages and other real-time conversation tools with traditional email.
"Users need to realise that these new features increase the attack surface on the Facebook platform, and make personal accounts all the more alluring for cybercriminals to break into," said Sophos senior technology consultant Graham Cluley.
"Facebook accounts will now be linked with many more people in the users' social circles -- opening up new opportunities for identity fraudsters to launch attacks," he added in a press statement.
Sophos noted that fraudsters are increasingly using hacked Facebook accounts to send spam messages -- compared with traditional emails -- because they are more likely to be opened by recipients lured to think the messages came from friends.
"Users also need to be aware that Facebook will be storing a complete archive of all their communications with one person. This raises concerns as to how this data could be misused if it fell into the wrong hands," Cluley said.
"With this in mind, it will be critical for Facebook to implement more effective filtering mechanisms to prevent fraudsters from manipulating Facebook users into falling victim to new spams, scams and phishing attacks."
Sophos called on Facebook users to take greater vigilance in securing their accounts, including installing hard-to-crack passwords, updating their computer security systems and being careful about which applications link to their profiles.
Facebook's new messaging system was launched on Monday and includes facebook.com email addresses.
Referred to inside the Palo Alto, California-based firm as "Titan," the service will be slowly rolled out in coming months to users.
Approximately 350 million of Facebook's more than 500 million members fire off messages using its existing service, with more than four billion digital missives sent daily, Facebook founder Mark Zuckerberg has said.
Market watchers say that with such a large user base, a free personalised facebook.com email service lays down a powerful challenge to the established email giants -- Microsoft's Hotmail, Yahoo! Mail and Google's Gmail.