A few members of Congress received threatening letters with a white powdery substance that was later found to be harmless. Apparently there has been a threat that 100 such letters will be sent out and 10 will have lethal powders.
source: http://www.reuters.com/article/2012/02/22/us-usa-congress-threat-idUSTRE81L21W20120222
source: http://www.reuters.com/article/2012/02/22/us-usa-congress-threat-idUSTRE81L21W20120222
