One cc2.8xlarge instance will give you 85 kH/s so 20 instances would give 1700 kH/s which only nets about $18 at current market prices / difficulty. So over 2 days he would have made off with a whopping $36.
Writing a script that generated $38 every time somebody accidentally commits a AWS key sounds like an amazing source of extra cash, depending on your current income.
If he would have used an altcoin that is limited by CPU like Primecoin he could have earned around 8000$ in 2days. Not sure if my calculation is legit through. It's based on the chains/day from the list at http://anty.info/primecoin-calculator/
Scary. I'm sure a lot of universities and servers will see an influx of hacks for coin-mining.
