Hoax tweet tests firms that filter social media fo

By Ryan Vlastelica NEW YORK (Reuters) - Firms that scour social media sites such as Twitter for information to help investors and traders make money faced their biggest test yet this week. A tweet reporting explosions at the White House appeared on the Associated Press's official feed Tuesday afternoon, sparking a temporary sell-off that briefly wiped out about $140 billion in market value on the S&P 500. The tweet was a fake and the account had been hacked. ...