Having a user open a file that happens to be infected with a zero-day flaw can just ruin your day. The bad news is that such flaws are on the rise, & not expected to level out anytime soon.

"Marco Peretti, chief technical officer at security firm BeyondTrust, agreed with the findings of the Sans Institute, urging users to follow the 'principle of least privileg'" in setting user access controls, permissions and rights. Peretti also suggested restricting or limiting the use of active code such as JavaScript or ActiveX in browsers."