The bogus, virtual, exists-only-in-cyberspace-game currency in some of these online games is fungible in the real world. Not only that, it is is more convertable than many meat-world currencies, since the means of exchange is completely open, voluntary, and not controlled by a central authority.
Sounds like World of Warcraft to me.
To be able to sell significant amounts of "gold" on ebay etc., people have to play the game a lot to "farm" it. Apparently, the game was initially balanced for a large fun factor, so getting gold and good items was no problem. However, the emerging market of conversion among "gold", "magical items", and dollars made some hardcore gamer wankers protest to Blizzard about the "farming" methods. That's no surprise since 100g could be sold for about $8, which is still a lot of money in China. In addition, hackers would try to generate their own items and sell them for dollars.
So, Blizzard became .gov and cracked down on "farming" and item exchange practices to prevent this "abuse", making the game a lot less fun for the average legal user, compromising software stability, instituting spyware and continuous monitoring, and also banning about 30,000 accounts per month on the basis of use of illegal items. So, if somebody sells you or gives you an item within the game, which happens to be flagged as counterfeit, you are automatically banned no matter if you even knew about it, thereby destroying many months of leveling on the experience treadmill. You can't protest, because customer service is overwhelmed with millions of users.
If the above sounds interesting to you as a curiosity, be sure to visit Amazon and read some customer feedback on the game. There are some amazing stories.