America's Federal Bureau of Investigation (FBI) is using a super-fast email scanning system dubbed "Carnivore" to covertly trawl through email messages in order to capture suspected criminals, reports the Wall Street Journal Tuesday.
The revelations have caused a furore among privacy and security advocates, because it requires a direct connection to a commercial ISP's network, giving the authorities, in theory, access to all Internet communications.
Carnivore is reportedly nothing more than a personal computer fitted with special software capable of scanning millions of emails in a second. According to the WSJ's report Carnivore, which was launched last year, has been used to gather evidence in fewer than 100 criminal cases.
In the US, a state or federal judicial order is required to carry out an Internet wiretap and it is usually possible to listen in on Internet communications via a traditional phone tap.
The FBI has reportedly justified the use of this technology as simply a more efficient means of carrying out surveillance.
"The burden is on the government to prove it has the right to do this," argues US civil liberties campaigner John Young.
Trawling communications data for key information is reminiscent of the international Echelon surveillance system that the US, UK and other nations are accused of operating covertly.
The UK government is currently trashing out the details of a law -- the Regulation of Investigatory Powers (RIP) -- that would require ISPs to install so-called "black boxes" directly connected to MI5's new Technical Assistance Centre.
Despite reassurances that these devices will only be used with a warrant, therefore legitimising the activity, privacy campaigners have voiced concerns that the technology could be abused.
Find out who's spying on you and how they're doing it in our exclusive Echelon News Special.