Back 2000 or so the project I worked on had a stand-alone e-mail system outside of the corporate system.
One of the freaking engineers, a guy who should have known better, got an e-mail from a "friend" with pictures of Anna Kournikova (the unbelievably hawt tennis player).
Except the pictures had a dot and three extra letters after the dot and g i f...
Those letters were... v b s. Anyone with a little experience knows that those are executable files -- visual basic script.
Walter was HIGHLY experienced. And he still clicked the file. And dropped our in house computer system for nearly a week.
Talked to one of the admins, and he said that when the virus got loose it immediately propagated to the e-mail list and started sending out multiple messages to everyone in the address book. A couple of other people also clicked the file, and it snowballed to the point where, at its worst, the various iterations were trying to send something like 1.7 million e-mails every second...