PRISM is the code name of a high-level clandestine surveillance program of the US National Security Agency.

Under the highly classified program, the U.S. National Security Agency and the Federal Bureau of Investigation have been tapping directly into the central servers of nine U.S. internet companies, extracting audio, video, photographs, e-mails, documents and connection logs that enable analysts to track a person's movements and contacts over time.

Earlier in June, Edward Snowden, a former CIA agent and contractor with the US' National Security Agency flew from Hawaii to Hong Kong and offered classified US government documents to media outlets, including London-based The Guardian. The documents revealed the existence of a high-level clandestine NSA surveillance program codenamed PRISM.

Whistleblower Snowden?said that the NSA has conducted more than 61,000 hacking operations across the globe, and Hong Kong and the Chinese mainland have been on the target list for years.

Several Internet companies have struck an agreement with the US government to release limited information about the number of surveillance requests they receive.

Facebook got 9,000-10,000 government data requests in second half of 2012; Microsoft got more than 6,000 US data requests in second half of 2012.