Brooks also confirmed she had a 'general update' discussion with David Cameron in 2010 on the phone-hacking scandal
Giving evidence to the Leveson inquiry today, Brooks said the story was "thankfully" not true and that the text messages were "on average, once a week" - and "maybe twice a week" during the 2010 general election campaign.
The Telegraph's Peter Oborne wrote in a recent column that Brooks "providentially retained the text messages she received from the prime minister, which I'm told could exceed a dozen a day".
Brooks told the inquiry today: "It's preposterous. One would hope the leader of the opposition or Prime Minister would have better things to do."
She added: "He would sign them off DC in the main. Occasionally he would sign them off 'lol' - lots of love - until I told him it meant laugh out loud and he didn't do that any more."
Brooks confirmed that she had discussed the News of the World phone-hacking scandal with Cameron in 2010. She said this was "no secret information, no privileged information, just a general update".
She said: "On occasion - and not very often, maybe once or twice - because of the news and the phone-hacking story kept coming up, we would bring it up, but in the most general terms.
"Maybe in 2010 we had a more specific conversation about it. It was nothing that he particularly wouldn't have said publicly but he was interested in the latest developments. It was to do with the amount of civil cases coming in and we had a conversation about it."