System Security Guard is a simple tool which checks the processes running on your PC for possible threats. If you've ever used System Explorer, then you'll be familiar with the program's core technology: essentially it just checks running processes and modules against its cloud-based database and alerts you to any potential problems.
Obviously this isn't the most sophisticated of malware detection systems. All the program can really do is compare files on your PC with files flagged as suspicious or dangerous on its own systems (and those ratings are community-based, so shouldn't be taken as always accurate). There's no extra behaviour monitoring, no checks on what a process is doing, and so no way System Security Guard can alert you to brand new, previously undiscovered dangers.
And there are no virus removal features within the program, either. So if it does highlight a possible threat, then you'll still need to figure out how to get rid of it yourself.
Still, System Security Guard is small, simple and lightweight. It's safe to run alongside other security packages. And if you suspect your PC is infected by something but your regular antivirus tool hasn't raised an alert, then there's no harm in running the program for a while: it just might help to identify the problem.