The group, which attacked sites in the US and Australia at the same time, left a boastful message including references to beer, sex, and Ferraris.
Pentaguard has been credited with 48 similar attacks on government and military sites across the world, including some in China, Romania and Vietnam.
UK sites affected by this attack were primarily in local government although a BSE inquiry website was also targeted.
Tony Lock, an analyst with Bloor Research said, "All the sites were running on hosted systems, which raises the issue of who is responsible for what is essentially a breach in security. More money, time and skills are needed to ensure that break-ins like these do not happen. There is a key skills shortage in this area and often a thorough solution is not implemented because it is too expensive."
He added, "I don't believe government sites are more vulnerable than commercial sites. In this instance, it was more a case of point scoring. If Pentaguard can crack government sites, just think what they can do to commercial sites."
The weakest links, according to hacker monitors attrition.org were: