Facebook users may want to take a closer look at their profiles – their default email addresses have likely been changed to @facebook.com.

Security vendor Sophos said this may be part of Facebook's efforts to make it more difficult for users to leave the social network.

"Clearly, this [is] all part of the site's plan to get more people using the @facebook.com email addresses, thus making the social network even harder to extricate yourself from," it said in a blog post.

But it also warned of the @facebook.com address soon being a target by cybercriminals.

"My guess is that it won't be long at all before we see criminals abusing @facebook.com email addresses for their own nefarious reasons," it said.

Facebook acknowledged it could have done better in informing users about the change, tech site Mashable reported early Thursday (Manila time).

Mashable cited a Wall Street Journal report saying a Facebook spokesperson admitted the social networking giant should have explained the email switch better.

“We want people to use whatever service is most effective for them,” the spokesperson was quoted as saying.

Sophos noted that while Facebook quietly announced last April it will give users @facebook.com email addresses to match their public usernames, it did not say it would make the @facebook.com address the default.

As such, a Facebook user's online friends will see the @facebook.com address as the default email address.

Sophos suggested Facebook users who do not want their @facebook.com email address to be displayed on their profile change your settings.

"Of course, you shouldn't be fooled into thinking that hiding your @facebook.com email address makes it impossible for someone to work out what it is. After all, it now matches the public username in your profile's URL," it added.

It also quoted Facebook as saying that by default, anybody on the site can send a user a message, and anyone on the internet can email the user at the new "username@facebook.com" address.

"Facebook will have to implement effective filtering mechanisms to prevent fraudsters from exploiting users with spam, scams and phishing attacks as a result of this opening up of the network's messaging system," it said. — LBG, GMA News