A UK law has been passed that makes it an offence to launch denial of service attacks, which experts had previously called "a legal grey area."
Among the provisions of the Police and Justice Bill 2006, which gained Royal Assent on Wednesday, is a clause that makes it an offence to impair the operation of any computer system. Other clauses prohibit preventing or hindering access to a program or data held on a computer, or impairing the operation of any program or data held on a computer.
http://news.zdnet.co.uk/security/0,1000000189,39284670,00.htm