The original problem went like this. When anyone started IE on the machine, it would start to connect to their homepage, then display an error:
It would then attempt to recover from this error by re-opening the tab:
However, this would immediately crash again, giving the same error as before. In order to avoid an infinite loop, IE would then stop trying to load up the website:
In a situation like this, there's a simple diagnostic test: try running Internet Explorer without any add-ons. To do that, go to:
Start | All Programs | Accessories | System Tools | Internet Explorer (No Add-ons)
When I did that, IE opened fine, and displayed the homepage without any errors. So, this proved that one of the add-ons was responsible. The next step was to determine which one. This machine had old versions of Java and Adobe Reader installed, so I upgraded them to the latest version in case it would help, but it didn't. It also had an old version of Flash, but the simplest way to update that is to go to the Adobe website, which I couldn't do while IE kept crashing.
In IE, I went to the Tools menu, then clicked "Manage Add-ons". Scrolling down the list, this one caught my attention:
The name was pretty generic ("Downloader Class"), but the publisher was "(Not Verified) BlizzardFly". The "Not Verified" bit means that the add-on hasn't been digitally signed; that doesn't necessarily mean that it's bad, but it's certainly a warning sign.
I couldn't find any useful information about BlizzardFly on the web; the nearest thing I could find was the Blizzard Downloader (used for World of Warcraft), but I don't know whether it's related.
Anyway, it was simple enough to test my theory: I disabled that add-on, then ran IE normally, and it worked fine. However, enabling/disabling add-ons is user specific, so anyone else who used that machine would also have to disable that add-on to stop IE from crashing. That's not ideal, so it's obviously better to remove that add-on altogether.
Clicking the "More information" link shown above wasn't particularly helpful:
Ideally I would be able to click the "Remove" button, but it was disabled. I then checked "Add/Remove Programs" in Control Panel, but this didn't appear in the list of applications, so I couldn't uninstall it that way. I then had a look in the Windows folder, and I found two relevant files:
The DLL file is the one mentioned above, i.e. the actual add-on. Running the uninstall program removed the add-on, although it didn't display any messages on completion. I then deleted these two files manually.
I wouldn't really class this as malware; my guess is that it used to work properly on an older version of IE, but it's not compatible with IE8. (I've seen similar problems with old versions of the Google Toolbar.)
Anyway, that machine is now working properly, which is good. In a situation like this, it's tempting to say "Meh, IE sucks, use Firefox/Chrome/whatever instead", but it's not really fair to blame Microsoft for problems caused by third party add-ons.