Mobile phone and broadband network O2 has jumped into the row over content providers sending out thousands of threatening legal letters, calling the practice "bullying". 

The main target of O2's wrath is ACS:Law, a law firm which specialises in sending out nastygrams to UK consumers, accusing them of downloading copyrighted material and offering a quick settlement out of court for around £500. Many people immediately pay up out of fear and embarrassment, especially as the accusations often involve pornography.

But many have called into question the systems used to identify the targets of these letters. Consumer group Which? says that it had messages from 150 people who claim to have been wrongly accused, and consumer rights group BeingThreatened has produced a handbook of advice for those who receive a letter.

O2 said: "Where we are legally obliged to provide information and the correct paperwork is presented, we will comply with the law. But we prefer the 'win-win' approach of encouraging the development of new business models that offer customers the content they want, how they want it, for a fair price".

Have you received one of these letters? Did you pay up, or have you attempted to fight it? Tell us your story, anonymously if you like, in the comments.