WINDERMERE, Fla. ( Stockpickr) -- Corporate insiders sell their own companies' stock for a variety of reasons. They might need the money for a big personal purchase such as a house or to fund a charity. Sometimes they sell as part of a planned selling program that they have put in place for diversification purposes, which allows them to sell stock in stages instead of selling all at one price. Other times they sell because they think their stock is fully valued. Some even unload their stock because they're worried about the future business environment and they think shares have downside risk.But they only buy their own shares for one reason: They think the stock is undervalued and has tremendous upside. The key word in that last statement is "think." Just because a corporate insider thinks his stock is going to go up, that doesn't mean it will. Insiders can have all the conviction in the world that their stock is a bargain, but if the market doesn't agree with them, it's not going to trade higher. Related: 5 David Tepper Stocks Buys for 2011 Recently, we've had a number of companies whose corporate insiders were buying large amounts of stock. These insiders are finding some value in the market, which warrants a closer look at these stocks. Here's a look at a number of companies whose insiders have been loading up on their own stock recently per SEC filings.