Arjen Kamphuis, a WikiLeaks associate and Dutch cybersecurity expert, has been missing for two weeks. The news of his disappearance was first made public when a friend, Ancilla van de Leest, posted on Twitter that he was missing and friends and colleagues were very worried about him, Huffington Post reported. Here is what you need to know about Kamphuis, his background, and everything we know so far about his disappearance.

1. Kamphuis Was Last Seen Checking out of a Four-Star Norwegian Hotel on August 20 After a Two-Week Holiday

Kamphuis, 47, hasn’t been seen since August 20, Huffington Post reported. He was seen checking out of his hotel in Bodø in northern Norway that afternoon, and was supposed to fly out of Trondheim to Amsterdam two days later. The train between Bodø and Trondheim takes about 10 hours, and it’s unclear where he disappeared from.

Update on the strange disappearance of @ArjenKamphuis. Arjen left his hotel in Bodø on August 20. He had a ticket flying out of Trondheim on August 22. The train between the two takes ~10 hours, suggesting that he disappeared in within hours in Bodø, Trondheim or on the train. https://t.co/t4OTJZGBeT — WikiLeaks (@wikileaks) September 2, 2018

WikiLeaks noted that Kamphuis might have disappeared in Bodo, Trondheim, or even on the train itself.

According to NLTimes, Kamphuis had just finished a two-week holiday in Norway.

The hotel he was staying at was a fancy, four-star hotel called Scandic Havet, Ad.nl reported.

2. Norway Has Put Its Elite Unit on the Search, but Friends Said Alarm Bells Didn’t Go Off Early Because Kamphuis Liked To Turn Off His Phone or Extend Vacations by a Day

Update #FindArjen; Arjen’s disappearance is all over the International news. We have spoken to press extensively. @ADnl, @telegraaf and others did a good job covering the story. We don’t have any updates to share right now. If anything changes I post it here first. Thank you all — Ancilla (@ncilla) September 3, 2018

Norwegian police officials told Agence France-Presse that they’ve started an investigation into Kamphuis’ disappearance. But they won’t speculate on what happened. Police are looking into whether his cell phone data can provide any clues, and are talking to people in the area to determine if anyone saw anything, NLTimes reported.

But as of September 4, no new information was known about what happened to Kamphuis, despite international attention on his disappearance, Ancilla noted on Twitter.

UPDATE: #ArjenKamphuis "We are at the very start of initial investigations. There are some leads we are checking out, but we have no firm theory at this time, " – Tommy Bech, operations manager Nordland County police – September 4th. #FindArjen pic.twitter.com/bFNk3bd5sU — Raymond Johansen (@RayJoha2) September 4, 2018

As of September 4, Norway had decided to put its elite unit, called “kripos,” on the case, Ad.nl reported. A translated quote from investigators reads: “At the moment there is no reason to assume that there is a crime, but we keep all possibilities open.” Kripos investigates organized crime and missing persons cases, and they have specialized technical and forensic expertise, Ad.nl reported.

His disappearance may not have triggered an alarm as early as others’ might because he wasn’t big on sending lots of photos of his holiday trips to friends, and missing meetings isn’t always a big deal for him, NRC.nl reported. In fact, he might turn off his phone completely or extend a vacation by a day. When he didn’t show up for a meeting on Monday and Tuesday, his friends became worried — especially since the Tuesday meeting was one he had initiated himself.

3. In May, Kamphuis Gave a TEDx Talk About Defending Yourself in a Digital World

Defend yourself in this digital world. No one else will do it for you. | Arjen Kamphuis | TEDxDelftArjen Kamphuis is a Digital Self Defence professional. Every day he helps people keep their secrets safe in the digital world. He has seen firsthand how government funded spying, hacking and security programs fall into the wrong hands and cause more harm than good. He argues that it is time we all start keeping ourselves… 2018-05-09T18:41:40.000Z

In May, Kamphuis gave a TEDx talk titled: “Defend yourself in this digital world. No one else will do it for you.” A TEDx talk is a talk given at a TEDx event using the TED conference format, but organized by the local community independently.

The TEDx video description describes Kamphuis this way: “Arjen Kamphuis is a Digital Self Defence professional. Every day he helps people keep their secrets safe in the digital world. He has seen firsthand how government funded spying, hacking and security programs fall into the wrong hands and cause more harm than good. He argues that it is time we all start keeping ourselves safe by taking responsibility for our own digital defenses and letting go of the idea that we’re just not smart enough to adapt. Arjen Kamphuis studied Science at the University of Utrecht and worked for IBM and Twynstra Gudde as IT architect, trainer and IT strategy advisor. He is a certified IT auditor and Information Technology expert (CISA, CISM). Since 2002, Arjen works for himself and helps managers, leaders and organizations realize the consequences of technological innovations. He is also involved in the national IT policy with regards to open standards and open source in the public domain. Although Information Technology takes up most of his time, Arjen likes to also be involved in scenario planning and exploring future strategies. He researches together with his clients the possible social, economic and geo-political consequences relevant to science and technology.”

In 2014, Kamphuis wrote “Information Security for Journalists,” a free handbook about protecting journalist communications from the government. You can read the handbook here. It’s been translated into Arabic, Chinese, French, Turkish, Spanish, and other languages, NRC.nl reported.

4. Kamphuis Is an Outdoors Enthusiast But Did Not Like Traveling in Dangerous Places Alone, & a Man Who Looks Like Him Was Seen in Alesund

#lost — Do you know or have you seen this guy? Arjen Kamphuis (47) from Amsterdam was last seen August 20 in #Norway and has been #missing ever since. In case you have any information or even saw him, please contact Dutch authorities at @Politie. Thank you. #MissingPerson Pls #RT pic.twitter.com/GCoVQU4ce7 — Mike Edward Moras (e-sushi) ?️ (@originalesushi) September 1, 2018

Kamphuis is known for being an avid hiker, according to friends and family. On Twitter, his bio reads: “Securing all the cybers, Free Software advocate, mountaineer, sailor, carpenter, geek and damn proud of it.” Some friends say that he might have gone on a hiking trip in the mountains in Bodo, VG.no reported. An article by Telegraaf, which is no longer accessible, said that his lates purchases had suggested he might have been preparing to go on a hike. Police, at first, had decided not to send an investigation team to Norway, believing he was hiking and would appear on his own.

However, friends told NRC.nl that although he is an avid hiker and mountaineer, he also likes to play things safe. Helma de Boer said he was not a daredevil and preferred to have companions with him if traveling in more dangerous places. “His style is better safe than sorry,” de Boer said.

Just realised that my red/black #Mammut gear may give ppl strange ideas about political loyalties. #FirstWorldProblems #Trumpocalypse2016 pic.twitter.com/8EUSWIQoxO — Arjen Kamphuis (@ArjenKamphuis) November 12, 2016

However, another unnamed friend told RTLNieuws that Kamphuis was an experienced hiker who may have decided to go for a hike in the area where he disappeared. The translated quote reads: “We suspect he was going to hike in the region, it is a well-known hiking spot, with very rough terrain.”

A man who looks similar to Kamphuis was seen in Alesund on Friday morning, according to tips received by authorities, VG.no reported. The police were notified, but it’s not known if this was really him or just someone who looked like him. Alesund is about 15 hours away from Bodo, according to Google Maps, although both are in Norway. It’s a little less than six hours south of Trondheim, his destination.

There was also an unconfirmed sighting in Ribe, Denmark.

Kamphuis is 1.78 meters tall and typically dresses in black. He wears glasses and has long, reddish blond hair.

5. Kamphuis Has Consulted with Julian Assange & Is an Expert in Cybersecurity Matters

Arjen Kamphuis – The IT of another Europe12 year before Snowden the EU already knew they should not trust US tech but chose to make itself more dependent on it anyway. We need a radical change in the way we select the tech that runs our society. The Stuxnet case and the revelations by Edward Snowden have shown how fundamental the problems… 2016-12-01T13:34:06.000Z

Kamphuis has consulted with Julian Assange. Computable refers to Kamphuis as being a good friend of Assange. He has also cooperated with and interviewed whistleblowers. He’s frequently cited as an expert in news articles, often commenting on open source software and the cloud.

He’s a known expert on cybersecurity matters, often consulting with journalists on how to keep their data safe from government intrusion. In June 2017, for example, Kamphuis helped the port of Rotterdam after it was paralyzed by a cyberattack. The translated version of the tweet below reads: “Last year, Arjen Kamp got the port of Rotterdam back to the talk, after it was paralysed by the biggest cyber attack ever. I still wonder: wasn’t there any newspaper that knew this? Or did they not feel it important enough to report?”

Arjen Kamphuis kreeg vorig jaar de Rotterdamse haven weer aan de praat, nadat deze was lamgelegd door grootste cyberaanval ooit. Ik vraag mij nog steeds af: Was er nou geen enkele krant die dit wist? Of vonden ze het niet belangrijk genoeg te melden? https://t.co/6jwf0iDoTP — Eric van de Beek (@beek38) September 1, 2018

In 2002, he co-authored a parliament motion that required all government IT in the Netherlands to have open standards. It became policy in 2007 and the Netherlands became the first western country to mandate open standards in public sector IT, CIS-India reported. After this, Kamphuis began lobbying for the same policy change in other countries. In the same interview, he said that in 2007 he and other experts rolled back a move to electronic voting machines in Amersterdam. “Through lots of media attention, a few spectacular hacks showing the technical insecurity of the systems, and legal pressure, we forced the government in 2007 to reverse the approval of the voting computers and go back to an all-paper balloting system. This reversal is part of a global backlash against electronic voting systems.”

Kamphuis studied science and policy at Utrecht University and worked as a Unix specialist for IBM, and a software instructor. He’s been an independent consultant for companies since 2001, CIS-India reported. This 2007 article concludes: “When not consulting Arjen is actively involved in (digital) civil liberties, the open source movement and criticizing the war on terror.”