Such software could be installed physically or remotely.
Another form of computer surveillance, known as van Eck phreaking, involves reading electromagnetic emanations from computing devices in order to extract data from them at distances of hundreds of meters.
Surveillance cameras are video cameras used for the purpose of observing an area.
The Snowden leaks have also revealed that the British Government Communications Headquarters (GCHQ) can access information collected by the NSA on American citizens.
Once the data has been collected, the GCHQ can hold on to it for up to two years.
Because the Snowden leaks demonstrated that American agencies can access phones anywhere in the world, privacy concerns in countries with growing markets for smart phones have intensified, providing a strong incentive for companies like Apple to address those concerns in order to secure their position in the global market.
Although the CALEA requires telecommunication companies to build into their systems the ability to carry out a lawful wiretap, the law has not been updated to address the issue of smart phones and requests for access to e-mails and metadata.