Classic Shell is absolutely safe - But ONLY if you download it from the Classic Shell website.
In fact I downloaded a classic shell installation package that had Sirefef or Babylon attached to it (Viruses).
I'll tell you why this happened: When we search for an app, we use Google. In Google, the ADS are on the very top, two or three results are ADS. You have to look carefully, and DO NOT CLICK the results that are not directly on the products' own website.
Always scroll down a little and look for the official sites.
So I had downloaded classic Shell from a 3rd party ad-site and it was INFECTED.
Also, and it is official now, that Google Toolbar is considered an actual VIRUS, ESET and others have elevated it to VIRUS, not merely Ad-Ware.
So, if you download an app, and it has Google Toolbar attached, your AV program will reject the download. Same goes with "ImgBurn" which is a great program in itself, but it has not just one but several viruses attached to it, you have to disable your AV, download, and always do the "Custom Install" - and OPT OUT of the garbageware.
Classic Shell as downloaded from it's own Site is clean, but always check for 3rd party crapapps attached to the installers you download.