FLC OF MD88 AT CRUISE NOTIFIED THAT THERE HAS BEEN A BOMB THREAT MADE VIA PHONE CALL. DECISION IS MADE TO DIVERT TO OKC. CTR IS NOTIFIED AND REQUEST IS GRANTED. APCH ASKS CONFIRM YOU ARE SQUAWKING 7500. FLC BELIEVES THIS IS A REQUEST TO SQUAWK 7500. CONSEQUENT CONFUSION HAS FBI STANDING BY BELIEVING A HIJACKER IS ABOARD AND CAUSED A DELAY WITH EMER VEHICLES.

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AT CRUISE (FL330) WE RECEIVED A MESSAGE FROM OUR DISPATCHER THAT A BOMB THREAT HAD BEEN MADE TO OUR FLT BY A PHONE CALL. AFTER QUICKLY DISCUSSING OUR OPTIONS AND CONFERRING WITH OUR DISPATCHER; IT WAS DECIDED THAT WE LAND AT OKC ARPT. I INFORMED ZKC THAT 'A THREAT' HAD BEEN MADE AGAINST OUR FLT AND THAT WE WERE REQUESTING DIRECT TO OKC AND A LOWER ALT. THE REQUEST WAS GRANTED AND WE TURNED DIRECT TO OKC AND STARTED A DSCNT. WHEN WE WERE HANDED OFF TO OKC APCH; THE CTLR ASKED: 'CONFIRM YOU ARE SQUAWKING 7500?' WITH ALL THE TASKS WE WERE ACCOMPLISHING AT THIS POINT THE CAPT DIALED 7500 IN THE XPONDER WITH A SIMULTANEOUS 'ROGER.' I PERCEIVED THAT APCH WANTED THAT CODE TO SEPARATE US FROM THE NUMEROUS OTHER TFC THAT WAS IN THE AREA. THE CAPT DOES NOT EVEN REMEMBER DOING IT. THAT'S HOW TASK SATURATED WE WERE. THAT XPONDER CODE BEING SET APPARENTLY GAVE THE WRONG MESSAGE TO ATC AND THE FBI. THEY THOUGHT WE HAD A HIJACK IN PROGRESS AND THIS DELAYED THE EMER VEHICLES APCHING OUR ACFT FOR SEVERAL MINS. IT WAS FINALLY RESOLVED AND THE END WAS UNEVENTFUL. I NOW REALIZE (LOOKING BACK) THAT APCH WAS ASKING IF WE HAD A HIJACKER WITH THE 7500 QUESTION. THAT QUESTION COULD HAVE BEEN MORE DELIBERATELY ASKED AND AT A SLOWER PACE. WE MIGHT HAVE CAUGHT ON. I ALSO SHOULD HAVE BEEN MORE CLR WITH MY INITIAL CALL TO CTR BY STATING 'BOMB THREAT.' I THINK THESE 2 FACTORS COMBINED; CAUSED CONFUSION TO ATC.