The original GT bot exploited mIRCís powerful scripting language, which included support for raw socket connections, to create a bot that was easily controllable via IRC. Functionality included, but was not limited to, port scanning, packet flooding, and provision of BouNCe.
The bot was open source (owing to mIRCís interpreted scripting) and easily configured. This attribute has allowed it to spawn a myriad of variants, many of which provide completely new functionality.
While the problem is currently understated and difficult to quantify, the trend is definitely on the up. Currently these pervasive bots are displaying worm-like ability and exploiting flaws in Windows or weak security. The two authors of one such variant were arrested in February 2003, with the UKís National Hi-Tech Crime Unit reporting that over 18,000 computers had been infected.
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