HONOLULU -- Thousands of dollars worth of counterfeit $100 bills are flowing into Hawaii, most likely from Los Angeles-based gangs, according to Secret Service officials.

For the last week or so, $2,000 to $2,500 a day in counterfeit $100 bills have been passed at retail stores in Waikiki and across the islands, the Secret Service said.

Some high-end Hawaii retailers are taking a hit.

"These are counterfeit $100 bills. They're being passed all over Waikiki as well as the shopping centers," U.S. Secret Service Special Agent in Charge Al Joaquin said.

The Secret Service believes at least four members of the Los Angeles-based Cryps and Bloods gangs are in the islands passing the phony money.

"What the passers are doing, they're buying expensive items and in a very short period of time they're returning items and of course getting genuine currency back," Joaquin said.

Law enforcement officials said the bills are being made on high-quality printers. They said the Cryps and Bloods have passed $5 million worth nationwide.

Some bills are getting by clerks even though they are using special pens that are supposed to detect counterfeit.

"In many of these cases, people said, 'Well, they passed the pen test.' Well, the pen test doesn't work. It's not good," said Tim Haverly, who runs security at the Marine Surf Hotel.

Both private security and the Secret Service said the pens are not reliable.

Check for watermarks when bills are held up to a light, Joaquin said. Make sure the image in the portrait area of the bill and the watermark are the same individual because some $5 bills are being made into 100s, he said.

"We have set out fraud alerts with security as well as (the Honolulu Police Department), and we feel confident that we'll have these individuals in custody before long," Joaquin said.

Along with the phony $100 bills from California, law enforcement officials said counterfeit bills are coming in through military personnel returning from the Middle East.