This particular fail was spotted by Abby Fuller, an Amazon employee who works at the company’s Amazon Web Services division.
She complained about the bug on Twitter, saying “this doesn’t seem right”.
“Logged into WhatsApp with a new phone number today and the message history from the previous number’s owner was right there?!
“And now I’m wondering how many other times it’s happened? Like does whoever has my old number now have MY WhatsApp history?”
Fellow Twitter users were quick to bombard her with questions – to see if she’d done something wrong, or to work out an explanation.
She replied: “Yes it was a new device. No it wasn’t second hand. It was not a second-hand SIM.”
“Yes I’m sure they weren’t my messages, or groups that I was added to.
“Yes they were in plaintext. I am sure it’s my phone number. It was not restored from a backup,” Fuller added.