This one is good too by some blogger in regards to

How it works

"This process can be used by hedge funds to either pump up a stock or to trash a stock but since I am using Herbalife as an example, we will discuss that situation. First information is widely distributed to make investors wonder about the company and to put fear into those longs that hold the stock. Next, high volume shorting takes place to drive the company's share price down.

As the short attack continues, more people parade out news to continue to put questions in the back of investors' minds. On a daily basis, shorts use computerized trading to control the direction of the share price. At opportune times, the shorts overwhelm the buyers (bid price) of the stock by selling short large number of shares to drive the share price down and to eliminate the buyers for the stock at that given time. For people who are not familiar with the bid/ask process of trading stocks, here is a  link to explain that process .

Shorts need to control the stock's share price over a long time (often several months to well over a year), and can't afford to just accumulate an unlimited number of short positions in the stock, so they have to be buying shares at the same time they are selling shares too. When the shorts drive the share price down, eliminating buyers as discussed above, some of those i nvestors trying to sell their shares at that same time will follow the share price activity downward lowering their ask price.

Now the shorts can buy back some of the shares they have shorted at lower prices including some shares where longs have put stop-loss sale orders to protect against downside losses. The shorts will only buy shares part of the way back up as the share price rises, and then wait to see if new buyers come into the market. If the share price continues to rise up to much again during the day, the shorts will repeat the same selling and buying process to control the share price.

As mentioned above, the shorts need to control the share price over an extended period of time. They need to wear down the longs with rumor mongering as well as by creating fear as the longs continue to see the share price go down from the computerized trading. They hope the longs will give up and sell their shares at the lowest possible share price.

Another observation, shorts try to wear down the longs by making sure that the share price closes down as many days in a row as they can put togethe r. At the close of each day, I witnessed volume dramatically increasing as the shorts tried to insure Herbalife's share price closed down. Shorts are hoping the longs frustration with the share price continuing downward will end up in capitulation where as many longs as possible just give up and sell their shares."