"Measures were taken to secure the area and ensure the safety of personnel," says a rep for CBS, whose studios are used to film the show. "Ultimately we were advised by the [Los Angeles Fire Department] that the substance was determined to be talcum powder."
The FBI declined to comment on Internet reports the letter may have been addressed to Dancing contestant Bristol Palin, whose ascent to the finals despite poor scores has generated controversy.
"Just as in any case, we don't confirm the identity of a victim based on privacy and security concerns," says FBI spokeswoman Laura Eimiller.
None of the celebrity contestants was rehearsing at the studio when the scare occurred. The show is broadcast on ABC but filmed at a CBS facility.