The S&P 500 was up about 1 percent at about 1,578 at 1:07 p.m. New York time today when a posting on the Associated Press Twitter account said there had been explosions at the White House and President Barack Obama had been injured. The benchmark gauge for American stocks erased almost the entire gain, falling as low as 1,563.03 by 1:10 p.m.

Lu Wang, Whitney Kisling and Eric Lam, Bloomberg – ‎Wednesday‎, ‎April‎ ‎24‎, ‎2013

Can this event be estimated using standard stress-testing approach? Probably, yes. Existing methodologies succeeded.