In its legal submission to the court last week, the firm said: "Blizzard's designs expectations are frustrated, and resources are allocated unevenly, when bots are introduced into the WoW universe, because bots spend far more time in-game than an ordinary player would and consume resources the entire time."

'Infringed agreement'

Blizzard argued that Michael Donnelly's tool also infringed the End User License Agreement that all parties have to adhere to when playing the game.

More than 100,000 copies of the tool have been sold, according to Mr Donnelly. More than 10 million people around the world play Warcraft.

Mr Donnelly said the first time had had been aware of potential legal action over his program was when a lawyer from Vivendi games, which publishes Warcraft, and an "unnamed private investigator" appeared at his home.

In his legal submission, he detailed: "When they arrived, they presented Donnelly with a copy of a complaint that they indicated would be filed the next day in the US District Court for the Central District of California if Donnelly did not immediately agree to stop selling Glider and return all profits that he made from Glider sales."

"Blizzard's audacious threats offended Donnelly," according to the legal papers.

Mr Donnelly says his tool does not infringe Blizzard's copyright because no "copy" of the Warcraft game client software is ever made.

Blizzard has said the tool infringes copyright because it copies the game into RAM in order to avoid detection by anti-cheat software.