A 19-year-old New Jersey man has pleaded guilty to knocking the Church of Scientology's website offline in a series of January 2008 online attacks.

Dmitriy Guzner, of Verona, New Jersey, was part of an underground hacking group called 'Anonymous' that has made the church a target of several attacks. He had been expected to enter a guilty plea when he was charged last October, but it was not formally entered until Monday, the US Department of Justice said in a statement.

He faces 10 years in prison on computer hacking charges and is set to be sentenced on 24 August in US District Court for the District of New Jersey.

The attacks began 19 January and managed to knock the Scientology.org website offline by hitting it with several bursts of unwanted Internet traffic. Called a distributed denial of service (DDOS) attack, it flooded the site with as much as 220Mbit/s per second of traffic.

Anonymous promoted the incident with several YouTube videos.

"For the good of your followers, for the good of mankind and for our own enjoyment, we shall proceed to expel you from the Internet and systematically dismantle the Church of Scientology in its present form," a creepy computerised voice says in one Anonymous video.