I do not know if Yahoo uses exploits in IE. One thing you will need to understand is the fact that IE is crippled ith exploits and websites may and can install spyware on users computers that are surfing the web using internet explorer.

While I may sound crazy but the fact is I had installed a software firewall on my computer and started searching for mp3's on the web using internet explorer.

I got bombarded with persistant popups but te scary thing was finding out that files in my internet cache where requesting internet access and running programs on my computer.

this is how many computers get spyware and adware installed.

the other way is shareware programs

read the end user license agreement for hints that additional components may be installed by third parties.
use firefox for now
http://www.mozilla.org/products/firefox/

it has great features and rules the web at the moment.