A notorious black hat says he has more than 200 million hacked Yahoo accounts for sale on the dark Web. The company says it is “aware of [the] claim,” but is refusing to comment on its veracity. Yahoo accounts are primarily used to log into the company’s webmail service, but also for other sites like Flickr.

It’s unclear at this point whether Yahoo has itself been breached, but the account data has been publicly available on a Tor-accessible marketplace called The Real Deal since Monday, and is apparently being sold by a hacker known as Peace, who has previously been linked to large-scale sales of MySpace and LinkedIn account details in 2012.

A Yahoo spokesperson said: