The details are covered very well by Orac, who says:

The favored laboratory of anti-vaccine practitioners and the “autism biomed” movement, a commercial laboratory known as Doctor’s Data is suing Steve Barrett, the man who maintains the excellent resource Quackwatch, for criticism Dr. Barrett leveled against it, criticism that Doctor’s Data richly deserved (in my opinion, of course).

Fighting these battles is extremely expensive and no legal defense funds exist for grassroots activists. Please blog about this to raise awareness and donate what you can to Quackwatch to help Dr. Barrett defend his right (and our rights) to tell the truth.