Mark Hypponen reported in Nov. 2006 that there were over 200,000. Last I'd heard there were about 360,000 total viruses (for all OSes: 30,000 for Mac, 15 for Linux, etc). I'd second guess the assertion of over 700,000 viruses, even with differences in counting variants and definitions of malware/spyware/adware/viruses/etc... I'm not personally familiar with this service, but I've not found many online scanners that do a real good job of scanning, let alone removing.

I have extensive experience with malware removal in a variety of environs, the tool I used most (though there is no ONE tool solution, I'd usually take 6-10 work hours per infected system and 5-10 different tools depending on infection type) was a hacked version of the NOD32 engine that did not need to be installed. I'd copy the latest defs from an installation of NOD32 (be ESET), copy the directory to the infected system and run the executable. It would find usually 90-95% of all infections on the system, and unless they were really deep, it could remove them all too. I'd also run the sysclean.com from trendmicro (pccillin engine) and then specific fixes/removal tools for specific persistent infections.