Lord McAlpine was falsely linked to a child abuse scandal, after an erroneous TV report on Newsnight. The report was proven to be untrue, and heads have rolled. However, allegations continued on Twitter, and McAlpine has asked the police to investigate.
It shows how serious allegations are online.
ThousandsMcAlpine generously offered not to pursue individuals with fewer than 500 followers for criminal offences under the Malicious Communications Act 1988, or the Communications Act 2003 - which makes 'improper use of a public electronic communications network' a crime. All he asked was that they made an apology and paid a nominal sum to Children in Need.
Newspaper reports claim that some have done so - but others have failed to respond. Now he has made a complaint to police - which could result in the individual prosecution of thousands of Twitter users who have not apologised. Some reports claim that up to 10,000 users could be at risk - after 1,000 people tweeted the allegations and 9,000 retweeted them.
If police take legal action, there could be a prosecution of thousands of people and fines. The law actually allows for imprisonment in very serious cases - for up to six months.
RisksIt goes to show that Twitter is not beyond the arm of the law. Users may think they have the freedom to say what they like online - and things they would never dream of saying in real life - but there are limits.
As McAlpine's solicitor, Andrew Reid, told The Mirror: "Twitter is not just a closed coffee shop among friends. It goes out to hundreds of thousands of people and you must take responsibility for it. It is not a place where you can gossip and say things with impunity, and we are about to demonstrate that."
CasesThere have been a series of cases relating to things said on Twitter, which have been deemed to have broken the law. One of the most famous was when 21-year old Liam Stacey, originally from Pontypridd, South Wales, was jailed for his posts about footballer Fabrice Muamba on Twitter.
Back in May Frank Zimmerman, 60, from Barnwood, Gloucester, was found guilty of posting aggressive, insulting and upsetting Tweets about Conservative MP Louise Mensch, during which he threatened her children's lives. He was found guilty of "sending Mensch an electronic message that was grossly offensive or of an indecent, offensive or menacing character".
And we have seen the first successful libel case in the UK too, when Justice David Bean found ex-chairman of the Indian Premier League Lalit Modi guilty of having libeled former New Zealand cricketer Chris Cairns on Twitter.
Be safeAttorney General Dominic Grieve recently issued a warning, urging people to understand the laws applying to Twitter, and ensuring they follow them.
At the very least, we ought to be asking some serious questions about what we are saying, whether it is true, fair and reasonable, whether it could be seen as malicious, and most of all, whether we would be comfortable saying it to someone's face.
Perhaps your mother was right after-all. If you don't have anything nice to say, don't say anything at all.