Former Daily Mirror editor Piers Morgan once told Jeremy Paxman how to access voicemail messages, the Leveson Inquiry has heard.
Newsnight anchorman Mr Paxman said he attended a lunch at Mirror headquarters in Canary Wharf in September 2002 where Mr Morgan teased Ulrika Jonsson about her relationship with former England football manager Sven-Goran Eriksson, saying he knew about a conversation they had.
Mr Paxman said Mr Morgan explained to him how to access people's phone messages after teasing the Swedish television presenter about the conversation.
Mr Paxman told the inquiry: "He turned to me and said 'Have you got a mobile phone?'
"I said yes and he asked if there was a security setting on the message bit of it. I didn't know what he was talking about.
"He then explained the way to get access to people's messages was to go to the factory default setting and press either 0000 or 1234 and that if you didn't put on your own code, his words, 'You're a fool'."
The BBC Newsnight presenter said he remembered the lunch for two reasons: he wondered why he had been invited and because of what Morgan said.
"Mr Morgan was teasing Ulrika that he knew what had happened in a conversation between her and Sven-Goran Eriksson," said Paxman.
"I don't know if he was repeating a conversation he had heard or he was imagining this conversation.
"To be fair to him I should imagine both possibly because he probably was imagining it."