I've been told my many computer geeks that Norton Antivirus actually contains spyware.
I've heard that rumor, too.
The one thing I took away from reading tons of material on various antimalware forums is that many people either love or hate Norton and McAffee... and that both cause problems is a fairly signifigant percentage of computers.
It may not be entirely their fault- there are so many combinations of hardware and software out there that some conflicts are inevitable.