Passwords, usernames and dates of birth for what appear to be 200 million Yahoo accounts have been put up for sale online.

The huge cache of personal data has been posted to a marketplace on the dark web by a cybercriminal with the moniker "Peace", who has previously sold millions of passwords and email addresses stolen from MySpace and LinkedIn.

Yahoo said it is "aware" of the claim that its customers' data is being sold online and is "working to determine the facts", including if the details are legitimate and if they were retrieved in a hack. The company, which sold to Verizon for $5 billion last week, has not confirmed a breach.

It is possible that the account details, which include scrambled passwords that require a key to be read, were obtained in an unconfirmed breach, or that they have been repackaged from other stolen data.