Web_speed - 9:17 pm on Feb 22, 2012 (gmt 0)
Could be email scrapers. These are win vb programs and they use the IE browser as a plug in. The visitor will be logged as a normal IE browser and the page (including java script/images/css) will be executed like in any IE browser.
I guess the only way to detect and separate them is to look for mouse movements as well as doing some other human/bot tests.
I've noticed a major increase in email spam across my domains lately. This may be a direct result of the above mentioned.