While Botnets have been a source of ire for security specialists everywhere, it seems that has not been the case for the NSA, which has apparently used them as spying tools.

The NSA has 'co-opted' more than 140,000 computers since 2007, using these devices as hosts for spyware, which would be injected into them.

According to a slide leaked by former contractor Edward Snowden, the intelligence agency used a technique called QUANTUMBOT. It searched out networks that had been compromised by a botnet and hijacked the control and command channel for the NSA's own use. The program had been described in the slide as "highly successful".

Sinking to their level

The slide is the first proof of allegations that the NSA had been hijacking compromised computers for its own spying programs and data harvesting operations. It showed that the NSA had looked to appropriating botnets to capture emails, browsing history and information from as many as millions of computers.

It did not say whether the efforts, which included impersonating social media websites like Facebook, were limited to computers overseas. There was also no data about whether botnets had been recaptured by criminals followed NSA insertion.

The NSA declined to confirm or deny the existence of the program.