Remember you can earn a premium if you lend your stock out or if you want to hedge your position ST against volatility you can only short with stock.
This has become common practice now as fund managers protect their position and hedge funds see a ST opportunity.
In fact RIO has the largest shorted position by value in the market at present $1.8B as at 9 Dec 2011. Even PNA has a $40M short position.
Nothing to be scared of IMO just market machinations at practice. Indeed, at some point covering will be triggered providing momentum to long only investors.
CDU Price at posting:
$3.93 Sentiment: Buy Disclosure: Held