Courtesy New York State Inspector General's Office

It was code, "a series of dots and dashes" etched into the sides of pencils, that cheaters used to take tests for a New York license to operate a school bus, a tractor-trailer or heavy equipment, federal and state investigators said.

Nineteen people have been arrested and charged in the driver's license scam, among them three security guards for the New York State Department of Motor Vehicles who were allegedly caught on surveillance cameras accepting cash bribes of up to $4,000.

Authorities believe as man as 250 commercial drivers licenses were issued to people who cheated and they are now being sought.

"It's potential school bus licenses, tractor trailers, tow trucks, tanker trailers, doubles, triples, the most dangerous vehicles on the road," said New York State Inspector General Catherine Leahy Scott, whose office was tipped to the alleged scheme by confidential informants.

Prosecutors released surveillance photos of what they said were suspects slipping cash into the pockets of DMV officials.

Three DMV security guards and eight others were charged with orchestrating the scam and accused by Loretta Lynch, U.S. Attorney for the Eastern District of New York, of enabling "unqualified drivers to take to our roads and highways behind the wheel of large buses and heavy trucks."

Eight people were charged with cheating on the commercial driver's license exam by paying cash for the pencils engraved with the coded answers or for a proxy to take the test.

"The eight commercial drivers who paid someone else to take their tests took the easy way out," said Manhattan District Attorney Cy Vance.

The DMV said it has strengthened its procedures and will eventually eliminate the paper test that was the focus of the scam.

"It is indeed unfortunate that people continue to look for ways to cheat on written tests," said New York State DMV Commissioner Barbara Fiala.