Mark Klein, the former AT&T technician who unveiled the NSA's secret surveillance operations, has died at the age of 79. In 2006, he disclosed that the NSA was tapping into internet traffic through a covert facility in San Francisco, confirming government access to data of millions of Americans. His revelations came in the wake of the post-9/11 surveillance expansion. Klein's disclosures prompted significant public discourse on privacy and governmental overreach, influencing future whistleblower cases, including Edward Snowden's in 2013. The Electronic Frontier Foundation confirmed his passing.