From the “If Mission Impossible* Were Being Remade Today” files https://www.stuff.co.nz/technology/digital-living/115560260/artificial-intelligence-first-voicemimicking-software-reportedly-used-in-a-major-theft:

Thieves used voice-mimicking software to imitate a UK company executive's speech and dupe his subordinate into sending hundreds of thousands of dollars to a secret account, the company's insurer said, in a remarkable case that some researchers are calling one of the world's first publicly reported artificial intelligence heists.

How was the scam exposed?

After the thieves made a second request, the director grew suspicious and called his boss directly. Then the thieves called back, unravelling the ruse: The fake "'Johannes' was demanding to speak to me whilst I was still on the phone to the real Johannes!" the director wrote in an email the insurer shared with The Washington Post.

*That’s the original classic TV series, not the movies, of course.