The serious Web site hack was spotted by Roger Thompson, chief research officer with AVG Technologies.
As of close of business Central European Time on Thursday, Thompson said the site was still pushing the fake software and infecting users without memory-resident IT security software.
The Reuters newswire, meanwhile, quoted a National Guard spokesperson as saying on Friday that the site was being taken down and would be securely restored to its former glory as soon as possible.
According to AVG's Thompson, the hacked version of the site offered users fake IT security software which alters users' Windows desktops, in an attempt to make them think their machine is infected, and asking them for $49.95 to "disinfect" the computer.
The bad news, however, is that the National Guard Web site also appears to silently infect a users' Windows machine with a rootkit application, which hides malware using a method which conventional IT security software finds it difficult to detect and erase.