A software company has won patents for software designed to prevent cheating in online games. Korea-based AhnLab was granted a patent for 'a method of sensing modification of internal time by a computer program' this week, the latest of several anti-hacking patents it has registered.

Popular multiplayer online games such as World of Warcraft, Counterstrike, and Battlefield 2142 have all suffered at times from hackers who alter program data in an attempt to gain an advantage over competitors. This has become a particularly serious issue for games like Warcraft, where in-game cash can be exchanged for real world currency, allowing hackers to generate substantial incomes. A Chinese student who reportedly sold more than $1.3m worth of Warcraft in-game items was recently arrested in Japan, for example.

Ahnlab's newly patented software is intended to prevent so-called 'speed hacks' or 'time hacks'. These alter the rate at which a gamer's PC clock runs. This may give the player advantages like faster movement or a faster attack rate. The patent was granted by the Korean Intellectual Property Office this week.

The patented anti-cheating technology is incorporated into AhnLab's HackShield application, which it licenses to online game developers and operators.

Users of the HackShield software include Electronics Arts, Sega of Japan and a number of Korean online game operators, AhnLab claims. The base licence price starts at $30,000 per year, AhnLab CEO Charles Kim told Game Daily last year.

However, HackShield has been criticized by game players who blame it for crashes and instability, and mocked by hackers who have claimed it is easy to circumvent.

Korean patent office records show that AhnLab is attempting to win local patents for a number of methods of protecting games from unwanted interference.

These include an application for a patent on 'method of diagnosing a malicious computer program', filed last year, but not yet granted (Korean patents typically take about 18 months from initial filing to registration or rejection).

That application includes the claim that ordinary players are deterred from playing due to the unfair advantage hackers gain, leading to a fall in player numbers and a corresponding loss of revenue for the game operator.

Ahnlab also has a patent for a 'method to cut off an illegal process access and manipulation for the security of online game client by real-time', which was registered in April 2005. This is for technology designed to prevent hacks which 'hook into' parts of the Windows operating system that handle keyboard and mouse input.

Hacks of this nature are commonly used to automate repetitive in-game actions, such as practicing a particular skill for hours in order to gradually improve a character's proficiency rating or to earn a steady income. As well as appealing to ordinary players, such techniques are also used by professional 'gold farmers' who control several characters simultaneously on numerous PCs.

Receiving a Korean patent gives AhnLab priority in applying for similar patents in other countries, if it chooses to do so within one year. Other software firms have also devised methods of detecting or preventing speed hacks and other common cheating techniques, among them US-based Even Balance, developers of the Punk Buster anti-cheat application which is used in several popular games. It's unclear if any of these methods have been patented.