The UK teenager accused of launching a denial of service attack on a US port told Southwark Crown Court on Thursday that he had no idea how the attack script got onto his computer.
The defendant, Aaron Caffrey, who was giving evidence for the first time during the trial, told the court he noticed the DDoS (distributed denial of service attack) script on his system "at some point in 2001".
Caffrey told the court he has been interested in computers for more than 10 years and considers himself to be an advanced programmer. He said he has written a number of Internet relay chat (IRC) client programs and co-wrote a script for the mIRC client that enabled it to "add colours and display text in different formats".
According to Caffrey, a new menu item that executed a script appeared on Caffrey's modified mIRC client, which he had published on his Web site. When he initially discovered the new link, he told the court he viewed it and realised it was "some sort of denial of service script".
Caffrey admitted to running the script only once, while his computer was not connected to the Internet. Afterwards, he said he unloaded the script from his mIRC client.
On the actual day of the attack, 20 September, 2001, Caffrey was not able to say if he was using his computer.
In early 2002, the Computer Crime Squad executed the attack script in a controlled environment. According to the Police, once the script is executed, it displays the message: "IIS Unicode exploiter coded by Aaron".
Caffrey denied he wrote the script: "I did not code the DDoS tool and I know plenty of Aarons," he said.
The case continues.