Corporate insiders sell their own companies' stock for a number of reasons.

They might need the cash for a big personal purchase such as a new house or yacht, or they might need the cash 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 overvalued and the risk/reward is no longer attractive. Some even dump their own stock because they have inside knowledge that a competitor is eating their lunch and stealing market share.

But insiders usually buy their own shares for one reason: They think the stock is a bargain 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 trade higher, that doesn't mean it will play out that way. Insiders can have all the conviction in the world that their stock is a buy, but if the market doesn't agree with them, the stock could end up going nowhere. Also, I say "usually" because sometimes insiders are loaned money by the company to buy their own stock. Those loans are often sweetheart deals and shouldn't be viewed as organic insider buying.

Stocks with notable insider activity is something that I tweet about on a regular basis. These are also the exact type of stocks that I love to trade and alert in real-time.

At the end of the day, it's institutional money managers running big mutual funds and hedge funds that drive stock prices, not insiders. That said, many of these savvy stock operators will follow insider buying activity when they agree with the insider that the stock is undervalued and has upside potential. This is why it's so important to always be monitoring insider activity but twice as important to make sure the trend of the stock coincides with the insider buying.

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.

ComScore

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One business services player that insiders are loading up on here is ComScore(SCOR) - Get Report , which operates as a cross-platform measurement company that measures audiences, brands and consumer behavior worldwide. Insiders are buying this stock into large weakness, since shares have fallen sharply by 33% over the last six months.

ComScore has a market cap of $1.6 billion and an enterprise value of $956 million. This stock trades at a cheap valuation, with a forward price-to-earnings of 16.3. Its estimated growth rate for this year is 822%, and for next year it's pegged at 29.2%. This is a cash-rich company, since the total cash position on its balance sheet is $146.99 million and its total debt is $33.04 million.

A beneficial owner just bought 120,000 shares, or about $3.27 million worth of stock at $26.96 per share. From a technical perspective, ComScore is currently trending above its 50-day moving average and below its 200-day moving averages, which is neutral trendwise. This stock has recently formed a double bottom chart pattern, after shares found some buying interest at $25.53 to $25.31 a share. Following that potential bottom, shares of ComScore have now started to spike higher right off its 50-day moving average of $27.31 a share. That spike is quickly pushing this stock within range of triggering a near-term breakout trade.

If you're bullish on ComScore, then I would look for long-biased trades as long as this stock is trending above its 50-day moving average of $27.31 a share or its 20-day moving average of $26.65 a share and then once it breaks out above some near-term overhead resistance levels $28.36 to $30 a share with high volume. Look for a sustained move or close above those levels with volume that hits near or above its three-month average volume of 511,262 shares. If that breakout hits soon, then this stock will set up to re-test or possibly take out its next major overhead resistance levels at $32.83 to its 200-day moving average of $33.36, or even $35 a share.

Chesapeake Energy

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An independent energy player that insiders are in love with here is Chesapeake Energy(CHK) - Get Report , which engages in the acquisition, exploration and development of properties for the production of oil, natural gas and natural gas liquids from underground reservoirs in the U.S. Insiders are buying this stock into massive strength, since shares have exploded higher by 141% over the last six months.

Chesapeake Energy has a market cap of $4.9 billion and an enterprise value of $15.5 billion. This stock trades at a cheap valuation, with a forward price-to-earnings of 7.8. Its estimated growth rate for this year -5.00%, and for next year it's pegged at 500%. This is not a cash-rich company, since the total cash position on its balance sheet is $4 million and its total debt is $9.65 billion.

A director just bought 350,000 shares, or about $2.12 million worth of stock, at $6.07 per share.

From a technical perspective, Chesapeake Energy is currently trending above both its 50-day and 200-day moving averages, which is bullish. This stock has been uptrending strong over the last three months, with shares moving higher off its low of $3.56 a share to its intraday high on Wednesday of $6.60 a share. During that uptrend, shares of Chesapeake Energy have been making mostly higher lows and higher highs, which is bullish technical price action.

If you're bullish on Chesapeake Energy then I would look for long-biased trades as long as this stock is trending above its 20-day moving average of $5.45 a share and then once it breaks out above some near-term overhead resistance levels at $6.75 to $7 a share with high volume. Look for a sustained move or close above those levels with volume that hits near or above its three-month average action of 41.30 million shares. If that breakout triggers soon, then this stock will set up to re-test or possibly take out its next major overhead resistance levels at $7.59 to $8, or even $9 a share.

Aaron's

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One services player that insiders are jumping into here is Aaron's(AAN) - Get Report , which operates as a specialty retailer of furniture, consumer electronics, computers, appliances and household accessories in the U.S. and Canada. Insiders are buying this stock into notable strength, since shares are up by 14.6% over the last six months.

Aaron's has a market cap of $1.8 billion and an enterprise value of $2 billion. This stock trades at a reasonable valuation, with a trailing price-to-earnings of 13.8 and a forward price-to-earnings of 10.3. Its estimated growth rate for this year 5.1%, and for next year it's pegged at 8.8%. This is not a cash-rich company, since the total cash position on its balance sheet is $242.24 million and its total debt is $493.51 million.

A director just bought 40,000 shares, or about $1.01 million worth of stock, at $25.29 per share.

From a technical perspective, Aaron's is currently trending above both its 50-day and 200-day moving averages, which is bullish. This stock has been uptrending over the last three months, with shares moving higher off its low of $20.50 a share to its intraday high on Wednesday of $25.66 a share. During that uptrend, shares of Aaron's have been making mostly higher lows and higher highs, which is bullish technical price action. That move has now pushed this stock within range of triggering a near-term breakout trade.

If you're in the bull camp on Aaron's, then I would look for long-biased trades as long as this stock is trending above its 20-day moving average of $24.55 a share or its 200-day moving average of $23.70 a share and then once it breaks out above some near-term overhead resistance levels at $25.79 to $26 a share with volume that hits near or above its three-month average action of 799,370 shares. If that breakout develops soon, then this stock will set up to re-test or possibly take out its next major overhead resistance levels at $27 to $27.69 a share. Any high-volume move above $27.69 will then give this stock a chance to re-fill some of its previous gap-down-day zone from October of 2015 that started near $36 a share.

TechTarget

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One technology player that insiders are active in here is TechTarget(TTGT) - Get Report , which provides specialized online content for buyers of corporate information technology products and services and marketing services for sellers of those solutions in the U.S. and internationally. Insiders are buying this stock into strength, since shares have risen by 18% over the last six months.

TechTarget has a market cap of $218 million and an enterprise value of $224 million. This stock trades at a reasonable valuation, with a trailing price-to-earnings of 41.9 and a forward price-to-earnings o 18.2. Its estimated growth rate for this year is -17.1%, and for next year it's pegged at 51.7%. This is not a cash-rich company, since the total cash position on its balance sheet is $42.77 million and its total debt is $49.65 million.

A beneficial owner just bought 118,481 shares, or about $992,000 worth of stock, at $7.79 per share.

From a technical perspective, TechTarget is currently trending above its 200-day moving average and below its 50-day moving average, which is neutral trendwise. This stock recently gapped-down big from around $9 a share to $6.73 a share with strong volume. Following that move, shares of TechTarget have started to stabilize and move sideways between $7.70 a share on the downside and $8.11 a share on the upside.

If you're bullish on TechTarget, then I would look for long-biased trades as long as this stock is trending above its recent range low at around $7.70 a share and then once it breaks out above some near-term overhead resistance at $8.11 a share with high volume. Look for a sustained move or close above that level with volume that hits near or above its three-month average action of 87,869 shares. If that breakout fires off soon, then this stock will set up to re-test or possibly take out its next major overhead resistance levels at its 50-day moving average of $8.41 to around $8.50 a share. Any high-volume move above $8.50 will then give this stock a chance to re-fill some of its previous gap-down-day zone that started near $9 a share.

Activision Bizzard

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My final stock with some decent insider buying is technology player Activision Bizzard(ATVI) - Get Report , which develops and publishes online, personal computer, video game console, handheld, mobile and tablet games. Insiders are buying this stock into big strength, since shares have trended up 28% over the last six months.

Activision Bizzard a market cap of $30.1 billion and an enterprise value of $32.9 billion. This stock trades at fair valuation, with a trailing price-to-earnings of 40.9 and a forward price-to-earnings of 18.8. Its estimated growth rate for this year is 49.2%, and for next year it's pegged at 9.6%. This is not a cash-rich company, since the total cash position on its balance sheet is $2.27 billion and its total debt is $5.03 billion.

A director just bought 20,000 shares, or about $795,000 worth of stock, at $39.79 per share.

From a technical perspective, Activision Bizzard is currently trending above both its 50-day and 200-day moving averages, which is bullish. This stock recently formed a double bottom chart pattern, after shares found some buying interest at $39.53 to $39.29 a share. Following that potential bottom, this stock has now started to spike higher back above both its 50-day and 20-day moving averages. That spike is quickly pushing shares of Activision Bizzard within range of triggering a big breakout trade.

If you're bullish on Activision Bizzard, then I would look for long-biased trades as long as this stock is trending above those recent double bottom support levels and then once it breaks out above some near-term overhead resistance levels at $42 to $42.45 a share and then above its 52-week high of $43.05 a share with volume that hits near or above its three-month average action of 9.53 million shares. If that breakout takes hold soon, then this stock will set up to enter new 52-week-high territory, which is bullish technical price action.

This article is commentary by an independent contributor. At the time of publication, the author held TK positions in the stocks mentioned.