Spy is such an ugly word.......And it actually a big blanket in a lot of thing.
Spying can be seen in 3 different level.
1.) Indirect apporach
2.) Direct Penetration
3.) Off-Site penetration
Most allies of the US are subjected to Indirect spying. Which include SIGINT (both COMINT and ELINT) however, the purpose to conduct intelligence surveillance is usually not to gather intelligence. But as part of Communication Security protocol. Where Japan and US have a direct communication system, that system needed to be test from time to time to ensure they are secure. One of the way is for friendly nation to try and hack thru the system by SIGINT, if they cannot gather anything, then the system is secure.
Do bear in mind, most country uses off-site penetration to steal intelligence. I don't need to hack a US DOD server to gather data for DoD, I can hack the computer the computer that server is connect to.
You can learn more about Communication Security here
Communications security - Wikipedia, the free encyclopedia