Legality
In the Police and Justice Act 2006, the United Kingdom specifically outlawed denial-of-service attacks and set a maximum penalty of 10 years in prison.
In the US, there can be a serious federal crime under the Computer Fraud and Abuse Act with penalties that include years of imprisonment. Many other countries have similar laws.
The US situation is under court ruling with a case in California.
Read more about this topic: Denial-of-service Attack