New York, Nov 10 (IANS) Ever got irritated when Facebook asked you to re-think a password for your account even if you typed in the one you have been using for years? That's because the social networking platform wants your account safe.

According to Facebook's Chief Security Officer Alex Stamos, the company buys passwords that hackers are selling in the black market and cross-references them with encrypted passwords used on their platform, tech website CNET reported on Thursday.

This, in turn, has kept the users' accounts safe from breaches.

"Keeping Facebook safe and keeping it secure are two different things," Stamos was quoted as saying at the "Web Summit" in Lisbon.

"Security is about building walls to keep out threats and shore up defences," but according to Stamos, safety is bigger than that. "It turns out that we can build perfectly secure software and yet people can still get hurt," he added.

According to CNET, when passwords are stolen en masse and traded on the black market, it becomes apparent just how many of them are the same -- "123456" and its consecutive numerical brethren are the main culprits.

If anyone is using one of these passwords, this automatically makes his/her account vulnerable.

Facebook provides a whole bunch of tools for users to make the security on an account nice and tight.