Every power in the world has spied on many others. It isn't just out of curiousity, but to satisfy a need to know what other countries, friend or foe, are doing that could somehow alter the balance of power in a region or worldwide.
The U.S. leads the pack with the National Security Agency (NSA), a colosal organization whose purpose is to scan the heavens for traces of signals that could identify threats to U.S. National Security. Detection and analysis of said signals would help identify the nature and scope of such threats.
In the process of scanning for signals, information can be captured which could be valuable to the United States and its allies. But also Information which Edward Snowden illegally extracted when he was working at NSA.
The NSA has also a facility for scanning for communications on an ample bandwith, which provides access to information of commercial use, such as email and internet.
Some of the bandwiths can be accessed by anyone with no limitations. Hence the protests from Brazil's lady President Dilma Rousseff