Aaron Caffrey had no idea of the consequences of the denial of service attack launched from his PC in September 2001.
The teenager's target was not the port of Houston, but Bokkie, a 17-year-old South African girl who had upset Caffrey by making derogatory remarks about Americans during a late night internet chat session.
Caffrey logged on to the chat session under the name Aaron X, shortly after midnight on 20 September 2001. Aaron X performed a "who is" command to discover Bokkie's IP address and fed the address into a denial of service programme.
The prosecution claimed Caffrey took pride in playing out the role of an "elite" hacker and said police found a website he was developing which contained denial of service software.
The Unicode vulnerability Caffrey exploited had been well publicised for a year and there was plenty of patch software available on the internet.
The prosecution said Caffrey's obsession with computers was a result of Asperger's syndrome, a form of autism characterised by difficulty communicating and an obsessive interest in specialist subjects.
When the attack launched by Caffrey's computer hit the port of Houston's web server, it left pilots without access to critical weather and tide information needed to steer large tankers containing oil and other potentially dangerous cargoes.
Caffrey said he knew about denial of service attacks and admitted he had been sent an exploit by friends but denied using it. He said denial of service software found on his machine could have been planted by hackers.