A THREAT by Sydney's Catholic Archbishop Cardinal George Pell to sue Twitter for defamation over an offensive tweet by the Melbourne blogger Catherine Deveny has revealed the increasing threat social media poses to the reputations of public figures.

While Cardinal Pell last night dropped his threat to sue over the tweet - which falsely suggested he condoned the sexual abuse of young boys - there was a call for the nation's defamation laws to be updated to reflect the new influence of social media.

Melbourne writer Catherine Deveny.

On Monday, Deveny posted a lengthy apology and retraction on her website after receiving an email from Twitter's legal department, alerting her to the threat.

During a Q&A debate on ABC on the existence of God last month, Cardinal Pell paused after saying: ''We were preparing young English boys … '' before adding ''for Holy Communion''.