The makers of World of Warcraft have struck back at the game's gold-farming black market, convincing PayPal to suspend the accounts of those using the service for gold-selling transactions. Warning letters went out this month.

Blizzard's complaint to PayPal accused gold-farmers of selling Blizzard's intellectual property, i.e. the virtual goods. PayPal's complied and sent notices to the gold sellers specified in Blizzard's complaint. The accused gold farmers were given a chance to appeal PayPal's finding by Jan. 21, otherwise they had to cease selling gold or face the suspension of their PayPal account.

The letter to the gold farmers, per WoW Insider:

You were reported to PayPal as an Intellectual Properties violation by Blizzard Entertainment Inc. for the sale of World of Warcraft Merchandise.

Warcraft Gold Farmers Get An Ultimatum From PayPalSIf you feel your sales do not infringe upon the intellectual property rights of the Reporting Party, please complete the attached Objection to Infringement Report by January 21, 2011.

The completed form should be faxed to the attention of the Acceptable Use Policy Department at [number removed] or emailed to [email removed].

Should you choose not to object to the report, you will be required to remove all World of Warcraft Merchandise from the website [url removed] in order to comply with the Acceptable Use Policy.

As an illicit market, it's difficult to measure the volume of gold farming business done globally. It's rumored to be upwards of $500 million in China alone. The PayPal action is viewed as a more cost-effective measure than lawsuits, especially as most of the offending gold sellers are outside of the United States.

Blizzard Strikes Gold Sellers With PayPal Notices [WoW Insider]