I find IE8 absolutely fine but everyone on here slams it - must admit though G Chrome gets my vote - Firefox for me is so jerky I cannot use it at all.
The way i see it is alot of exploits seem to be mainly aimed at IE. I saw a video a few days ago about XSS and it mentioned some things that could only be done through IE such as stealing things from the victims clipboard and a few other things. If the victim uses a different browser it would stop some of these things.
I find that quite often sites display well in FF but in IE they look different. I don't mean to the point they look messy but to the point you look at it and think, it shouldn't be like that. Additionally i find FF to be faster then IE and i find it alot more customisable. To many average Internet users they probably don't see anything wrong with IE but when you try other browsers and compare them you will find that other browsers are better in most ways compared to IE. The amount of users using IE has been dropping while the users for the other browsers are increasing. That kind of speaks for itself.
Not to mention websites that block Javascript and such (like MySpace, for example) can still be exploited in IE, because if you put a new line through the word Javascript (\n), MySpace won't pick it up and will allow the code to go through. Most browsers won't execute the code because of the line, but IE will still read it as "Javascript" and execute the code.
So if there's something malicious going on, IE is most vulnerable.