For the past five years, British spying nerve-center GCHQ has been port scanning internet-connected computers in 27 countries – in a exhaustive hunt for systems to potentially exploit.

That bombshell comes amid fresh leaks detailing the dragnet surveillance programs operated by the Five Eyes nations: America, UK, Canada, Australia and New Zealand.

German publisher Heise reports that the HACIENDA program scans open ports on all public-facing servers to seek out vulnerable systems – a basic reconnaissance strategy adopted by countless hackers and other curious folk.

As well as simple port scans, GCHQ also stashes the banner text sent by some server software to connecting clients, and other data.

Assuming the server is telling the truth, these banners can be useful because they typically declare the version number and name of the software – this is information that can be used to look up exploits for known vulnerabilities in the code. And we all know GCHQ et al love vulnerabilities.

The Heise report – co-written by Snowden confidantes Jacob Appelbaum and Laura Poitras – states HACIENDA sits besides GCHQ's previously exposed program of tapping trans-Atlantic fibre-optic cables:

The process of scanning entire countries and looking for vulnerable network infrastructure to exploit is consistent with the meta-goal of 'Mastering the Internet', which is also the name of a GCHQ cable-tapping program: these spy agencies try to attack every possible system they can, presumably as it might provide access to further systems. Systems may be attacked simply because they might eventually create a path towards a valuable espionage target, even without actionable information indicating this will ever be the case. Using this logic, every device is a target for colonisation, as each successfully exploited target is theoretically useful as a means to infiltrating another possible target.

The HACIENDA database is shared by the UK's GCHQ with other members of the Five Eyes spying club. And HACIENDA allows spies to set up basecamp on the networks of other countries before launching attacks. "So-called Operational Relay Boxes are used to hide the location of the attacker when the Five Eyes launch exploits against targets or steal data," Heise explains.

The article goes on to suggest various counter measures against all this port scanning. One of these techniques – TCP Stealth – has been put forward to the IETF as a draft standard.

Port scanning software, such as nmap and Zmap, are standard issue tools for hackers, developers, students and anyone else with a sense of curiosity; the only things noteworthy about HACIENDA is its scale – The Register first reported on the UK's £1bn "Mastering the Internet" surveillance project in 2009.

Internet security experts are neither surprised nor impressed by the latest news. "Five Eyes have their own non-public Shodan and they are using it," security expert the Grugq noted somewhat dismissively, referring to the well-known Internet of Stuff's search engine. ®