The defacements are being carried out by loose-knit hacking groups that meet in several online forums to coordinate their attacks. One hacker, called Cold Z3ro claims to have hacked nearly 5,000 Web pages, Warner said.

Web defacement community took off in the militant Muslim community in 2006 when hundreds of Danish Web sites were hacked after a Danish newspaper printed cartoons depicting the prophet Mohammed. One group, which had about 70 members at the time of the Danish cartoon incident, now boasts more than 10,000 hackers, Warner said.