IT technicians at the leftwing daily Taz say spying on colleagues had been going on since the beginning of 2014

“As a small boy,” wrote Sebastian Heiser in a recent blogpost, “I always thought adults know everything … I couldn’t wait until I was finally able to understand how the world worked myself.”

But Heiser, 35, appears to have gone too far in his erstwhile virtuous quest to understand the world, after being revealed as a spy at the centre of the leftwing, ad-free daily, Taz, where he was a staff reporter.

The intrigues that have rocked the usually staid world of German newspapers began last month when a so-called “key-logger” stick – a USB-style contraption that hoovers up all the information on a computer, including passwords and everything else tapped into its keyboard – was discovered in a computer in the newspaper’s newsroom in central Berlin.

An IT technician was strategically placed in the room to pounce on whoever might try to retrieve the key. When Heiser – a “well-liked but dogged reporter with a huge amount of self-confidence” according to one colleague – turned up to work, he is reported to have surreptitiously placed a newspaper over the back of the computer in question and withdrawn the keylogger. His colleagues reportedly watched in disbelief as they peered at the goings-on over their screens.

When confronted and forced to hand over the keylogger, Heiser denied everything other than that he had simply been withdrawing a USB stick. Shortly afterwards, he was escorted out of the building after handing over his office keys, according to the newspaper. The editorial staff reacted with shock when informed of the affair by their editor-in-chief, Ines Pohl, who warned all staff to change their passwords – they had, potentially, been spied on, she said. Anything they had typed into their computers could have leaked.

“We’re dealing here with an espionage affair. We’re all deeply shocked,” Pohl wrote last week. “The basic trust in the Taz – both internally and externally – has been shattered this past week.”

The scandal has been dubbed #tazgate. The conservative press in particular has drooled over the drama at a paper known for its tongue-in-cheek headlines and alternative points of view. One daily summed up the events in its own attempt at humour as: “The Spy Who Logged Me.”

IT technicians have established the device had been used to hack into and steal data from at least 16 staff accounts within the editorial department and that the spying – including trawling through journalists’ emails – had been going on since the start of 2014.

Days before he was escorted from the Taz, Heiser revealed an alleged sting he carried out on the liberal daily Süddeutsche Zeitung (SZ).

Heiser was employed by the Munich-based newspaper’s services supplement, which covers a range of topics from career, to real estate, pensions and finance to energy and wine.



But he claimed that the supplement broke its own editorial guidelines that articles had to remain independent from advertisers, alleging that topics were motivated by how much advertising they could bring in, rather than their editorial value.

“Their rule of thumb was that for every quarter-page advertisement (back then around €20,000 plus tax) an entire page would follow, discussing the advertisement’s topic,” he wrote. In a particularly damning incident, he said one article that indirectly advised people how they could reduce their tax by having a foreign bank account, ran in tandem with an advertisement for an Austrian bank.

“It’s a blatant advertisement for tax evasion by the Süddeutsche Zeitung,” Heiser wrote, “because in exchange it will receive a handsomely paid advertisement from the Tirol Sparkasse bank.”

In other allegations against the paper, he says he was forced to tone down criticism of certain financial products and to prettify the language on others.

Heiser’s evidence includes protocols from editorial meetings and voice recordings that he secretly taped without his colleagues’ knowledge. His findings, he said, led him to resign from his job in apparent disgust and disillusionment after just 10 weeks.

Heiser explained he went public with his claims now, years after leaving the paper, because he was outraged by what he called the “hypocrisy of the Süddeutsche Zeitung’s indignation over tax evasion” as it “paraded itself as the assault-gun of the tax office”. He made his claims just as the paper was reporting the HSBC tax evasion scandal.

The SZ has strenously denied the allegations, which have been dubbed #SZLeaks elsewhere and generated huge interest in Germany. Heiser has been condemned for his actions at the SZ by some. “No journalist can sniff around for months in the style of the NSA,” said media lawyer Markus Kompa. But Kompa also added that, as an investigative reporter, Heiser had made many enemies and he hinted that the culprits for the spying might yet be found outside the Taz.

But others hailed him as something of a hero after the SZ leaks, a “German whistleblower” (a word that has come into the German language since Edward Snowden). But then came #tazate and his reputation has taken a spectacular dive.

Heiser has not responded to Guardian requests for an interview, nor to those from a range of German newspapers. According to the Taz, the journalist – described by colleagues as a fearless lone operator – failed to turn up for a meeting at the paper to discuss his alleged actions. The newspaper is now taking legal steps against Heiser, who had appeared to have a glowing career before him, having uncovered several scandals in the political and business worlds.

As IT specialists continue to assess the damage, the paper has to hope that its informants and interviewees are reassured by its statement that the “Redaktionsgeheimnis” – the protection of sources – remains sacrosanct. The editor is determined to show any details they have given the paper are in good hands. “We need to win back the trust,” she said.