DALLAS >> A North Texas man accused of sending more than 500 hoax letters that contained a white powder to schools, government offices, day care centers and other locations in the U.S. and around the world was arrested Monday, federal authorities announced.

Hong Minh Truong, 66, made his initial appearance in Dallas federal court after he was arrested and charged in a criminal complaint with false information and hoaxes.

“While it was determined that the mailings did not contain toxins or poisons, each incident required a field screening of the letter’s contents, which cost taxpayer dollars and diverted first responder resources,” Diego Rodriguez, special agent in charge of the FBI’s Dallas office, said in a statement.

A judge ordered that Truong — from the Dallas suburb of Rowlett — be held in custody until a detention hearing on Aug. 4.

Truong’s attorney did not immediately return a message Monday.

According to the criminal complaint, Truong is accused of sending more than 15 batches of letters from the Dallas area, starting in 2008. In all but two of the batches, a white-powder substance was put in the envelopes.

The hoax letters were mailed to cities across the U.S. and to U.S. Embassies abroad. Most recently, some letters were mailed to hotels in the vicinity of this year’s Super Bowl in New Jersey.

Investigators focused on Truong after an IP address associated with him was identified after 28 public schools in Boston received letters in June 2013, according to the complaint.