When does the use of an employers’ computer network for personal purposes become a criminal offence? That’s the question surrounding the case of Aaron Blosser, who is now facing a jail sentence as a result of a program he unleashed while working as a contractor at US West in Denver. Blosser is an enthusiastic supporter of the Great Internet Mersenne Prime Numbers Search, mathematical mavens who spend all their spare time looking for ever larger prime numbers. Just the sort of challenge to throw at the formidable processing power of US West’s network. Blosser is adamant that his program only ran when the processors were idle but the company claims that it disrupted directory information services, and searches of the databases were taking a minute instead of the usual 15 seconds. Blosser’s home has been raided by the FBI and his computer equipment confiscated. While he hasn’t been charged yet, US West is pressing for prosecution in a case which could set an important precedent.