Initial field tests from a letter received by a Florida abortion clinic have come back positive for anthrax spores. However, field tests produce many false positives and false negatives, so the accuracy of the results is unknown. More sophisticated tests have been ordered and more definitive results will be available tomorrow. More than 170 reproductive health clinics received letters claiming to contain anthrax yesterday. The letters were signed by the Army of God and bared a return address from the U.S. Secret Service or U.S. Marshall Service. Abortion clinics are urged to be on high alert for suspicious packages and contact local and federal law enforcement should they receive such threats.