Yahoo!
Gmail stopped the practice in late 2017.
This is the largest known data breach of its kind.
'We apologise for the mistake.'
It's distinct from the breach announced in September.
500m users' data was stolen by hackers.
It's not clear what the government was looking for.
Both companies are encouraging people to change their passwords.
It could be the single largest cyber-breach in history.
The site's owner Yahoo! is the centre of a bidding war.