| The increase in supply is not caused by the final net position. It's in what you see when you look at the market. Suppose there are 100k shares issued. Some traders decide to naked short 50k. Actual holders of the shares say, "Oh crap. Half the company is for sale - better dump my shares while I still can." So they put up a total of 75k for sale. Now 50k of the 75k of actual shares need to be purchased by the people selling short, but if you look at the total number available for purchase at that point, you'll see 125k shares for sale - more than were ever issued. Of course, this same issue can bite the short sellers in a "short squeeze". Suppose we own 60k of the shares in the company. If we see someone selling 50k, we know they are doing a naked short, and we should buy it. When we do, we will own 110% of the company. Obviously, to make things go to 100%, the short sellers need to buy the remaining 10% of the shares from you. You get to pick the price. * Edited to add - you can see a recent example of a short squeeze in Volkswagen around October 2008: http://www.reuters.com/article/idUSTRE49R3I920081028 |
With naked short sales, you're removing the supply restriction, making it possible to continue to pressure the stock downward beyond where it should go in a balanced market. This sort of pressure can cause a panic among investors in the company and become a self-fulfilling cycle - once a company's stock is pushed below a certain level, many investors will dump the stock, regardless of the fundamentals of the company. It's not a cheap maneuver, but it's potentially phenomenally profitable for the people committing the short, and it's totally devastating to the company under attack. It also doesn't represent balanced market sentiment, nor the actual value of the company, and the company can be forced to take dramatic measures due to circumstances for which it wasn't to blame. It's a potentially highly destructive practice and banned for a very good reason.