Photoshop. Top ten with a bullet.
1. Must be very common (lots of people effected) tick
2. Must be bad at what it was designed to do (AV that doesn't, etc) tick
3. Must be misunderstood (users should have the impression that it's good) tick
4. Must effect the computers general operation (running at machine startup is almost required) tick
5. Cannot actually be nothing but a Virus/Malware (must attempt to actually do something useful) tick
Footnotes:
On item (2) yes, Photoslug does actually edit images, and the final result can be very good indeed - but given (a) the incredibly bad user interface, making it impossible for the non-expert to achieve anything of worth in any reasonable timeframe, and (b) the incredibly poor performance, we can tick this box with confidence.
On item (4), yes again. When running, it sucks resources like there is no tommorow. It's not a system start-up hog in the clasic mould, but it is in some ways worse than that. Because it takes such an incredibly long time to load, you are forced to open it and then leave it open, because you cannot sensibly close it anytime you are not using it for a short while, as the next time you need it you will have to endure the dreadful start-up time again. As the final insult, you can't flick-start the lengthy start-up process and carry on doing some other useful task while you are waiting for it, because it grabs the system focus repeatedly, meaning that during that interminable period, you can't use Photoslug, and you can't use anything else either!
Did anyone mention Vista yet? Yes, well that one is covered then. Good. But Photoslug bothers me more than Vista. At least with Vista you can use XP instead. Between them, Adobe and Corel have seen to it that you have no alternative to using Photoslug.