Many people are concerned about European citizens who have returned after fighting in Syria or Iraq. Above, supporters hold an ISIS flag in 2014. Getty Images

ISIS just got even darker. The extremist Islamic State group, believed responsible for the deadly terror attacks in Paris last week, has launched its first propaganda website on the dark Web, as authorities and activists try to shut down its online infrastructure. In the days since the attacks, which killed at least 129 and left dozens more critically injured, authorities have focused on how the extremist group has been communicating, with many claiming it is using encrypted messaging servicing to avoid detection. But there's been no evidence that this is the case to date, with some reporting coordination for the attacks was done simply through unencrypted SMS.

One way the group -- also known as ISIS, ISIL, IS and Daesh -- is attempting to avoid surveillance is by utilizing the dark Web, and while ISIS has been active on the hidden parts of the Internet for some time, the heightened scrutiny after the Paris attacks pushed it to establish a website there.

ISIS dark web webiste  Tor
What the ISIS propaganda website looked like on the dark web before it was defaced and taken offline. Screengrab

The dark Web is a part of the Internet not indexed by Google and only accessible through a specially modified version of the Firefox browser called the Tor browser. The benefit of using the Tor network is that the identities of visitors to a site are anonymized, and those running the site are also shielded from view. The reason ISIS has moved to the dark Web is that its surface Web presence has been knocked offline by a combination of law enforcement, ISPs and the work of online activists using the banner of Anonymous.

Earlier this week, Anonymous launched what it called its biggest campaign to date to tackle ISIS online, targeting both websites and the group's social media presence, even going so far as to publish a "How To" guide for newcomers. The group claims it has so far identified tens of thousands of Twitter accounts associated with ISIS, as well as knocking some websites offline, including one claimed as a recruitment website for the group.

However, the implementation of the dark Web site has left anyone visiting it open to being identified. While the site itself is hosted on the dark Web, some of the videos on the site are still hosted on the surface Web, meaning those playing the videos are leaving themselves open to identification.

When International Business Times visited the site through the Tor browser, we were warned the site was attempting to capture "HTML5 canvas image data," which can be used to fingerprint your browser's unique setup and therefore track and identify users, a tracking technique about which the Electronic Frontier Foundation has warned.

The ISIS website is a mirror of the one on the surface Web by the group's official publication arm, the Al-Hayat Media Center, featuring an archive of content from the group including videos, articles and pictures. The group also links to its extensive social media networks, including Telegram, the secretive network ISIS recently has been utilizing.

Telegram Wednesday announced it had removed 78 ISIS-related conversation channels across 12 languages in response to intensified scrutiny since the Paris attacks, with some suggesting ISIS used the app to communicate. While Telegram claims to be an encrypted messaging app, researchers have shown there are significant weaknesses in its implementation of encryption.

While the new dark Web site is the first such "official" site established by ISIS, the group and other terrorist groups like it have been utilizing the anonymous nature of the Tor network to help raise funds through bitcoin donations as well as allowing the group to buy guns easily, even within the EU, where gun controls are very strict. A report by the European Union Institute for Security Studies published in June also revealed training manuals, including "Terrorist’s Handbook" and the "Explosives Guide," were also distributed on these invite-only terrorist forums.