certificates security in internet explorer - store

Dear all,

I wonder how secure is storing private key and certificates in internet
explorer certificate store.
Can anyone point me to the wab pages where description of the protection of
these store on the hard drive is published?
Can anyone point me to the web page with info (or descibe it here) if there
is/was a virus or worm that attacts this store or in any other way steals
the private key stored on the hard drive?

Or is it just smart card that makes you sleep well?

Thank you very much, I need to include this in my lecture for the
students...
Mitja