The US Federal Bureau of Investigation (FBI) and information security experts announced that unknown persons hacked into the bureau's mail system on Saturday, sending tens of thousands of fake messages warning of a possible cyber-attack.

The FBI confirmed the report of the independent security group The Spamhaus Project, which indicated that a large number of fake emails were sent in two batches early Saturday from a secure FBI server.

In a statement, the bureau and the Department of Homeland Security's Cybersecurity and Infrastructure Agency said they were "aware of the incident... involving fake messages from the @ic.fbi.gov email account."

"This is an ongoing situation, and we are unable to provide any additional information at this time. We continue to call on the public to be vigilant against anonymous senders and urge them to report any suspicious activity," the statement added.

The following chart shows email traffic originating from the FBI mailserver (https://t.co/En06mMbR88 | 153.31.119.142) involved.

You can clearly see the two spikes caused by the fake warning last night.

Timestamps are in UTC.

pic.twitter.com/vPKvzv74gW

— Spamhaus (@spamhaus) November 13, 2021

For its part, the "Spamhouse Project" said that some of the fake messages sent on behalf of the Cyber ​​Threat Detection Group of the Department of Homeland Security were titled "Urgent: A Threat Factor in Systems."

The messages warned recipients that they were the targets of a "sophisticated" cyber attack by a "known extortion gang".

Independent security expert Brian Krebs said he also received a fake email from an FBI email address, but it contained a different message.

It was not immediately clear whether the party that sent the fake messages had access to this server, or that they were hackers from outside.

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