I dont think that this is a question that will ever be answered 100%.
IE8 is as secure as any Browser in my opinion, providing you allow all patches etc and you have decent Security System installed. I mainly use Firefox however, as I like the way it saves passwords.
The main problem on the Internet, is the amount of people on it that havent got a clue what they are doing. I recently sorted out a friend of mines computer; this man had run a number of succesful businesses, but didnt even know what a firewall was!
These are the idiots that spread viruses etc.