Today, the FBI says countries from the Asia-Pacific region are the ones most likely to attempt to gather intelligence about U.S. military operations in Hawaii.
China would have the biggest interest, followed by Russia, Cossa said. North Korea would be interested but doesn't have as many resources.
Their targets? Pacific Command is the U.S. military's headquarters for the Asia-Pacific region. The Navy, Air Force, Army and Marine Corps also each have their own headquarters for the Pacific on Oahu. The National Security Agency keeps an intelligence center tucked away in central Oahu.
There's a major missile defense testing site on Kauai. A high-powered missile defense radar capable of tracking a baseball-sized object 2,500 miles away — called the Sea-Based X-band Radar — visits Pearl Harbor regularly.
These days, computer hacking and cyber espionage — the area Bishop was working in most recently — are major spying methods.
Eyes and ears are useful too, whether they belong to undercover agents or to businessmen, tourists and students who may share what they see with their governments.
Honolulu has nearly 1 million residents, and the state is a mecca for sun-seeking tourists from around the world. This makes Hawaii an easier place for intelligence gatherers to blend in than, say, remote parts of Wyoming where the U.S. keeps ballistic missiles.
Pressure to gather intelligence from the islands is likely growing as the Obama administration places a greater emphasis on the region with the military's "pivot" to the Pacific. Cossa said the policy "shines a big target" on Hawaii.
"I'm sure every intel guy in China has been told 'Get more details. What does it really mean?,'" said Cossa, who spent 26 years in the Air Force, including three tours at Pacific Command.
The reconnaissance goes both ways. On the other side of the Pacific Ocean, the U.S. is eager to gather its own intelligence on new ships, planes and other equipment China is adding to its military.
Cossa said allegations like those against Bishop make for flashy headlines but account for a small percentage of the spying going on.
Most of the espionage involves people trying to listen to phone conversations and hack into email and computers, he said. It's easier for people to steal information this way and it's harder to detect.
"Obviously if you're working with classified information in the military, in Hawaii, you should expect somebody is trying to listen, someone is trying to copy," Cossa said.