The World of Warcraft downloader has been updated after disgruntled players accused Blizzard of using it to steal their bandwidth.
A change introduced in the recently released patch 1.10 meant that the downloader ran constantly - even if the program was closed.
In a post on the Blizzard forums, WOW player Buronimo wrote: "So I was playing Wednesday morning after installing the 1.10 patch and in the middle of playing my firewall says that Blizzard Downloader is trying to make an outgoing connection.
"Ummm why? I already have the patch, what is it doing?"
A Blizzard poster going by the name of Tseric replied: "When you are done downloading the patch, the connection will stay open allowing you to upload the patch to others. Basically, you become part of the network allowing other players to download the patch easier.
"This is how Bittorrent has been working for some time, as a sort of 'pay it forward'-type setup."
Tseric was careful to point out that "You aren't actually sending out any information other than the patch content."
But many WOW players still weren't happy. A poster called Glorinus argued: "The simple fact is, is that I NEVER agreed to be a patch mule for Blizzard and you never informed me of this fact when I signed up (nor have you updated the Terms Of Service)... You knowingly piggy-backed software onto my computer without my knowledge, thus it should be considered spyware.
"Seriously guys, you make over 30 million a month in North American subscriptions and you have to pull this kind of snakish BS on your loyal and paying customers?"
Fellow poster Nexoccultus echoed Glorinus' comments, stating: "No you can't use my bandwidth for your stupid bit-torrent crap. Buy some file servers."
Following the complaints, Blizzard has now updated the downloader with an option you can use to stop it running in the background. To find out more, visit the official World of Warcraft website.