Did you accidentally friend a North Korean hacker on Facebook?

North Korean hackers have been preying on potential targets using Facebook, but the company has thwarted at least some of their activities.

Last week, Facebook joined Microsoft and others in the security community to disrupt a covert campaign, the White House said on Tuesday. The scheme involved creating fake personal Facebook accounts that attempted to build relationships with potential targets and coordinate other activities.

In a statement, Facebook confirmed its involvement and said the Lazarus Group, a hacking collective that many security experts suspect works for North Korea, was behind the fake accounts. "We also notified people who may have been in contact with these accounts and gave suggestions to enhance their account security," Facebook said.

It isn't clear why North Korean hackers targeted Facebook users. However, social media is often ripe with people's personal information, including email addresses, phone numbers and location data. In this case, North Korea may have sought to trick their victims into installing malware, which could then be used to take over their computers.

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Microsoft, meanwhile, has disabled accounts linked with the attack, and bolstered its antivirus software to prevent reinfections.

"Microsoft acted before the attack in ways that spared many US targets," President Trump's homeland security adviser, Tom Bossert, said at a Tuesday briefing.

The news comes as the US on Monday publicly blamed North Korea for launching the WannaCry ransomware attack that infected over 200,000 computers in May. Microsoft said it reached the same conclusion.

"If the rising tide of nation-state attacks on civilians is to be stopped, governments must be prepared to call out the countries that launch them," Microsoft President Brad Smith said in a statement.

Little is known about the Lazarus Group, but the elite hackers may have been involved in the Sony Pictures breach of 2014, as well as several attacks on banks.

For internet users, it's a good idea not to accept friend requests on Facebook or LinkedIn from those you don't know. Even legitimate-looking accounts can be fake. Placing too much personal data on your social media page can also leave you vulnerable to hacking schemes.

This article originally appeared on PCMag.com.