Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of oil and gas explorer QEP Resources (NYSE:QEP) jumped as much as 10% today after a new investor was disclosed.

So what: Activist investor Jana Partners disclosed a 7.5% stake in the company and has plans to unlock shareholder value. Jana has held talks with QEP management, and is reported to be calling for moves including breaking out one segment of the company.

Now what: When activist investors get involved it's tough to know where the company will head. Jana Partners is arguing that management hasn't done enough to unlock the company's value, although QEP did create a master limited partnership to sell some assets earlier this year. I don't think an activist move like this is a reason to buy the stock or a reason to change your investing thesis. However, it might force management to make some changes, although these deals have resulted in both success and failure for activist investors.

Fool contributor Travis Hoium has no position in any stocks mentioned. The Motley Fool has no position in any of the stocks mentioned. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.