I can reason not supporting older versions of IE because they had such a problem with rogue extensions (Browser Helper Objects and Toolbars) *and* render content differently than other browsers, including newer versions of IE. Blocking newer versions of IE that render content the same as any other browser and that have essentially 'fixed' a lot of the extension problem by making users aware of what extensions are present is nonsensical though.

Also note that NOT ALL SSL ROOT CERTIFICATE AUTHORITIES ARE PRESENT IN ALL BROWSERS. The newer CA efforts for cheap or sometimes free SSL certs, for instance, certainly are not. The root CA not being present in IE may be the issue here. Without it, every SSL protected page would cause a huge warning. UPDATE: Not the case, at least not with latest IE.

And note that when two files or sets of data 'match' as mouser eloquently explained it (much better than I), that is what is called a 'collision', as I tried to explain above. Thus, the collision rate is paramount when determining what algorithm you want to use.

If it need be secure, then you want an essentially zero collision rate, but that comes with high computational complexity and a large bitspace. Thus, in *my* rogue thinking, I prefer to call such 'secure hashes', digests. A digest is a hash, but a hash isn't always a digest. Of course, being irreversible is another important characteristic that applies to both forms. Anyway, it just makes it easier to differentiate.

Update: I see mouser did put (collision) is parenthesis. In retrospect, my explanation assumes the reader knows too much already.