A massive denial of service attack has disabled some of the world's largest virtual goods trading sites. The Korea-based sites hit by the attack are responsible for a substantial portion of the country's estimated $1bn trade in virtual gold, weapons and other items for games like World of Warcraft.

    Spokesmen for some of the trading sites affected, which include ItemBay, ItemMania, ItemPF and ItemRia initially claimed that they were offline for technical reasons, local media report. Later, ItemRia admitted in an online notice that the outages have been caused by a flood of traffic, apparently directed by hackers. An ItemPF spokesperson has since made a similar admission, according to local media.

    The sites have been difficult or impossible to access for at least the past four days, according to Korean media (links are in Korean). Error messages returned suggest that servers are overloaded or have been deliberately taken off line.

Chinese 'blackmail' claim

    Local press reports have blamed Chinese hackers for the attacks, citing claims from unnamed online security sources that the torrent of unwanted incoming traffic originated from large numbers of Chinese internet addresses.

    In the past, malicious hackers have used denial of service (DoS) attacks from botnets to extort money from commercial website operators. Local media have claimed that blackmail is the aim of the current wave of attacks. The sites affected reportedly handle more than 90 percent of Korea's online item trading - a business now worth more than $3m a day, according to Korean government statistics.

    Several of of the virtual item trading sites hit in the current attack also suffered an unexplained intermittent outage over several days at the end of September.

    Players use the item trading sites to buy and sell gold, weapons and other items from massively multiplayer online games. Players do this because they do not wish to repeat sections of the game they have already played, or because they lack the time - or in some cases, the skill - to obtain these items by simply playing the game. Some sites also offer services such as rapidly increasing a character's level or experience points with round-the-clock play by skilled players.