According to the warning, MacGuard is simply a clone of a Windows app called WiniGuard. The company releasing the software, Innovagest 2000 SL, may be using the credit card numbers they harvest during the purchase process for "nefarious purposes."
WiniGuard "hijacks the user's desktop and typically displays exaggerated or false claims of spyware found to frighten the user into paying for the program," according to Sunbelt Malware Research Labs.
While our fine readers wouldn't get suckered into such a scheme, parents, grandparents, aunts and uncles might not be so educated. If you know someone with a Mac who might fall for this, do them a favor and forward them this warning.
The MacGuard website is at macguard.net.