Have a gander courtesy of gawker & YouTube:
Tom Cruise has personally, PERSONALLY, been pwned. This weekend, an anonymous Internet group (named Anonymous — these are not masters of subtlety) started a war with the Church of Scientology by hammering the group's web site; Scientology.org is down after a brief traffic spike. This isn't the only group of Internet users unafraid of the intimidating cult; a whole range of sites has turned the Church into a mockery by doing what mainstream celebrity-coverage outlets wouldn't dare. Here's a guide to the war (and a creepy manifesto made by The Internet!).
This loose group of Internet vigilantes (vaguely centered around, but not officially connected to, the site 4chan) often harasses unsavory but small-time people, but they did help with the arrest of pedophile Chris Forcand. Their usual tactic is a simple denial of service attack like the one against Scientology.org, but they occasionally get more sophisticated; members tell me they plan to hoist banners above some Church branches. Inspired by the release of Tom Cruise's secret Scientology video and the Church's attempts to suppress it, Anon promises an all-out war in the following hokey but entertaining video: