From the ArcaMax Publishing, Jokes Newsletter:
http://www.arcamax.com/news/jokes/s-363907-584375
Any time you use a computer, it looks like work to the casual
observer. You can send and receive personal e-mail, calculate your
finances and generally have a blast without doing anything remotely
related to work.
These aren't exactly the societal benefits that everybody from the
computer revolution expected but they're not bad either.
When you get caught by your boss--and you will get caught--your best
defense is to claim you're teaching yourself to use the new software,
thus saving valuable training dollars. You're not a loafer, you're a
self-starter.
Offer to show your boss what you learned. That will make your boss
scurry away like a frightened salamander.