(CBS 8) - A Virginia mom was horrified when her child was attacked by a drug sniffing dog at Dulles Airport.

The dog bit her 4-year-old child and wouldn't let go.

Customs and border protection says the dog was in the middle of a training exercise and is unclear what triggered the attack. The agency says it will take steps to keep it from happening again.

News correspondent Surae Chinn has the story in this video report.