You Can't Control Activist Investors, but You Can Control What You Do About Them
Very few companies find themselves on an ever-improving business path. It's way more common for a business to cycle between good times and bad times, especially if it has been around for a long time.
Sometimes, usually when a business is having a tough time, an activist investor will show up and take a large stake in the company with the hope of spurring management and the board of directors to improve performance in some specific ways.
If this happens to a company you're a shareholder in, you'll need to think carefully about what this means for you.
Source Fool.com