I would also lean on the side of that it is users trying to disguise themselves as using IE for their browser for terms of compatibility. I have done it several times myself due to websites that say something along the lines of 'to view this webpage you must use IE', and yet I know the website will work perfectly fine in another browser...

So I have done this, and yes often times it uses an older version of IE for telling what it uses (as xboxrulz has said above).

But yes it is also possible that there is a spam bot of some sort....

It really could be almost anything really....there isn't any 100% way to tell exactly what it is.

Well I haven't experienced a huge number of record additions in my MySQL databases or anything like that. I don't think it is a spam bot registering on my forms.

I sure find it strange though, every other month doesn't have requests from IE4.