Twitter mistakenly flagged the well-known BBC (British Broadcast Channel) as "materials obtained through hacking". A simple link sharing would result in a flagged Tweet:
Kevin Beaumont, a security researcher at Microsoft, obviously found out somehow about the Twitter flag on the BBC and tweeted a simple link to the BBC's main website with the addition "Guys check out the new hacking site, BBC News".
Twitter uses a special policy for "distribution of hacked materials". This policy is then applied on Tweets pointing to a site which has fallen under that policy. Whether the BBC was reported by a user or a Twitter-internal algorithm decided to flag BBC is unknown.
Not even one hour later, the Tweet of Kevin now appears "back to normal", as all flags were removed by Twitter.