Because the feature was exploited by a powerful TrojanWorld of Warcraft is one of the most popular games at this time because it allows you to play online with other players from all around the world. As you might know, the game enables you to create a character that will improve its power, level and other abilities by fighting and exploring the world. Because many players already gained a huge experience, they decided to sell their character's items on auction sites like eBay.
Although this is quite a good deal for every gamer that already played World of Warcraft or other similar game, it seems like eBay banned the auctions of virtual goods such as character's items because some clients used Trojan files to steal private information from other WoW owners.
The issue was first identified by F-Secure, a company that developed the well-known antivirus solution and reported it to the auction service that took the decision to block this kind of transactions.
Stealing other World of Warcraft character items was quite a profitable activity because many eBay sellers rated their products at about $64.99 per 50 gold on certain servers so imagine that multiple stolen accounts means more money.
"There are numerous password-stealing trojans specifically designed for World of Warcraft and other massively multiplayer online games. The passwords are used to steal gold and other items from victims so that it can be re-sold online. Now eBay has decided to ban the auction of virtual goods. Actually, it's a more aggressive enforcement of already existing policy. It should be interesting to see just how this change in the re-sale market affects the source of supply," F-Secure's employee sustained in a blog post published on the official site.