http://beginnersinvest.about.com/cs/...s=penny+stocks
http://stocks.about.com/cs/regulator...tm?terms=OTCBB
"Companies most susceptible to the pump and dump technique often possess the following qualities: they are listed on the loosely regulated Over the Counter Bulletin Board (OTCBB), the stocks trade infrequently, and the companies possess a small public float. Stocks with a small float have low levels of outstanding stock that is available for public trading on a day-to-day basis, are more tightly held by a small group of insiders (who may, in fact, by the perpetrators of the pump and dump themselves), and for these reasons, are much more volatile and easy to manipulate than a liquid stock on a major stock exchange."