Norman Malware Cleaner is an interesting portable antivirus tool which will scan your PC, detecting and removing any malware that it uncovers.
The program is very easy to use. Just download and launch it (patience may be required, it's a 275MB file), click the Start button and it'll immediately run a Quick Scan, checking your Registry and running processes for any sign of threats. This took only 75 seconds on our test PC, so you won't have long to wait, and anything Malware Cleaner finds will be immediately quarantined to keep you safe. (If this turns out to be a mistake then you can restore it from the Quarantine tab.)
Need a more thorough check? There's also the option to scan the most common file types for malware, every file on your system, or just a particular folder.
And clicking the Options tab reveals some useful settings. Check "Enable rootkit cleaning" and the tool will attempt to remove any rootkits it finds, for instance, while clearing "Enable archive unpacking" may greatly cut the time required to run full scans.
You don't get any real-time protection here, and it's not possible to schedule scans, so Norman Malware Cleaner is no substitute for a full antivirus package. If you think you might be infected by something and your regular security software can't help, though, then the program could be very useful: you should be able to run Malware Cleaner on any alongside other antivirus programs without conflicts, and it'll quickly give your system a security health check.