They're at it again.

Yesterday, General Electric (NYSE: GE) suffered a brief-but-painful $3.5 billion loss of market cap. The reason: A duo of corporate activists-cum-funnymen known as the "Yes Men" issued a press release aimed squarely at the company's $14.2 billion reported 2010 profit ... and the $3.2 billion tax refund the Internal Revenue Service sent GE on that profit.

According to the release, which The Associated Press picked up and distributed as fact, GE wanted to help repair the gaping hole in the U.S. budget. Hence, it was returning the IRS' check uncashed. (In fact, the IRS never actually issued GE a check. The "tax refund" was more of an internal accounting matter.)

That's neither here nor there, of course. What's important is that investors saw GE gifting away $3 billion or so of their cash, and promptly subtracted an equivalent sum from GE's market cap. It's not the first time this has happened. In 2004, the Yes Men similarly snookered Dow Chemical (NYSE: DOW) investors by impersonating a company spokesman in an interview with the BBC and promising to gift $12 billion to victims of the 1984 Union Carbide-Bhopal disaster, which prompted a selloff of that stock, too. In 2007, they targeted Exxon Mobil (NYSE: XOM) when they appeared at a Calgary oil and gas conference to announce the company's new human-remains-derived fuel source, "Vivoleum." Last year, the Yes Men generated peals of laughter at Apple's (Nasdaq: AAPL) expense by needling the company's use of "conflict minerals" in its iPhones.

Who's next? Who knows. But if and when your company becomes the Yes Men's next target, and whether or not you "get the joke," here's what you need to remember: Bad news, whether true or false, is temporary. By definition, long-term investors should not react to it on impulse, but put the same time and effort into considering selling a stock as they did before initially buying.

In illustration of which -- after selling off steeply in the wake of yesterday's news -- GE shares recovered briskly, ending the day down only a few pennies from where they began. But that didn't help traders who "sold at the bottom." Make sure that when the Yes Men strike again, you don't end up the butt of the joke.

Fool contributor Rich Smith has no position in any stocks named above. The Motley Fool has a disclosure policy. Try any of our Foolish newsletter services free for 30 days. Apple is a Motley Fool Stock Advisor recommendation. The Fool has written puts on Apple. Motley Fool Options has recommended a bull call spread position on Apple. The Fool owns shares of Apple and Exxon Mobil. Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors.