BALTIMORE ( Stockpickr) -- Key corporate insiders sell their own companies' stock for a plethora of reasons. They might need the cash 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 level. Other times they sell because they think their stock is fully valued. Some even dump their stock holdings because they're worried that economy could go sour and they want to lock in profits.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 or her 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 could end up going nowhere. Related: 6 Heavily Shorted Stocks That Could Explode At the end of the day, it's large institutional money managers running huge mutual funds and hedge funds that drive stock prices, not insiders. That said, many of these savvy money managers will follow insider buying activity when key insiders are snapping up shares. Recently, a number of companies' corporate insiders have bought 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.