Former U.S. National Security Agency contractor Edward Snowden got Microsoft, Google and Yahoo to upgrade computer security against hackers. The companies are adopting safer code to protect their networks and data, after years of largely rebuffing calls from the White House and privacy advocates to improve security. The new measures come after documents from Snowden revealed how U.S. spy programs gain access to the companies' customer data.

Google, Yahoo, Microsoft and Facebook provide data to the government under court orders. At the same time, they are trying to prevent the NSA from gaining unauthorized access to information flowing between computer servers by using encryption.

The NSA has tapped fiber-optic cables abroad to siphon data from Google and Yahoo, circumvented or cracked encryption, and introduced weaknesses and back doors into coding, according to reports in the Washington Post, the New York Times and the U.K.'s Guardian newspaper based on Snowden documents.

Microsoft's networks and services were allegedly hacked by the NSA, the Washington Post reported Nov. 26. Documents disclosed by Snowden suggest that the NSA targeted Microsoft's Hotmail and Windows Live Messenger services.