A California lawyer has filed a potential class action lawsuit against the internet search company Yahoo.
The California-based company has not commented
Stephen Galton says he was subject to a "barrage of harassing, defamatory and abusive messages" from anonymous users on a Yahoo message board.
Mr Galton, who wants other users to join in the suit, has accused Yahoo of sheltering users who harass people in cyberspace.
The California-based company declined to comment.
A spokeswoman for Yahoo said: "It wouldn't be prudent for us to comment on this pending lawsuit."
Mr Galton, a partner in legal firm Galton & Helm, registered to use Yahoo message boards to respond to a post criticising one of his clients.
His defence of his client led to him being subjected to name-calling by other message board users.
When the company refused to reveal the details of the message board users who allegedly harassed Mr Galton, the lawyer sued the company for the information in April.
He sought the names, addresses and phone numbers of his critics from Yahoo, but he says it provided only partial information.
George Godar, a technology partner at law firm DLA, said US laws makes it straightforward for people who believe they have been defamed to find out who is behind online nicknames.
Typically, he says, a complainant sues a fictitious defendant, usually "John Doe", and then issues a subpoena to make a net firm release the real name of person behind the disputed postings.
When presented with a legal document most net firms will hand over details of users and subscribers, he says.
"People rarely look at things like privacy policies," says Mr Godar, "and most companies will have a specific exception which says if they are compelled by law to hand over information they will do so."
The Recording Industry Association of America has used this willingness to share subscriber information to gather details of users it considers to be illegally sharing pop music.
Mr Galton's lawsuit has been launched to make Yahoo hand over more information about people who posted the allegedly offensive messages.
He also alleges that Yahoo does nothing to give redress to people who have suffered abuse via its message boards.
He is now urging others who have been the target of such attacks over the past four years and made fruitless efforts to find out who posted messages or get them removed to join him in a class action lawsuit.
One of the consequences of the publicity Mr Galton has received over the lawsuit has been to have his e-mail address and telephone number posted to message boards.
In many countries net firms are granted so-called "common carrier" or "immunity from suit" status that removes their legal responsibility for what their users do online.
However, this legal protection usually evaporates if a company is put on notice about websites or messages that infringe laws but does nothing about them.