This certainly is good news, but the scope of the task should not be underestimated. Between mid-2015 and early 2016, Twitter shut down 125,000 terrorist accounts. Keep in mind that those were just the ones that could be identified as terrorist-related (mostly affiliated with the Islamic State). Twitter noted that “there is no ‘magic algorithm’ for identifying terrorist content on the Internet, so global online platforms are forced to make challenging judgment calls based on very limited information and guidance.” Further, the same users could quickly open new accounts.

For most of us, these four companies constitute the Internet universe that we venture into for our personal use. But beyond this level of the Internet are zones where terrorist groups do their most serious business.

Those whom we might call “top-level terrorists”—among them the leaders of Islamic State (IS) and Al Qaeda and their subsidiaries—survive because they are quick to adapt to changes in the physical and virtual battlespace. For some of their online communication, this has meant moving from the easily accessible “surface web” to the “deep web” and then on to its deepest part, the “dark web.” This is where one can find drugs, pornography, weapons, and other contraband. The dark web is out of reach of the most common search engines, such as Google, and is difficult for hackers to penetrate. IS warehouses its propaganda videos and other material on dark sites, and has raised and transferred money using the dark web’s currency of choice, Bitcoin.

Similarly, IS has relied on Telegram, one of the encrypted communication tools that provides enhanced security for texts and other messaging, to relay instructions to its supporters, such as how to find a particular dark web address. In 2015, Telegram began featuring “channels” for specialized content, which IS promptly started using. During one month in 2016, 700 new IS-related channels were opened. One such channel was “Mujahideen Secrets,” which provided indoctrination and information for prospective “lone wolf” terrorists.

Another challenge the Global Internet Forum faces is in its effort to produce counter-messaging that is effective in offsetting terrorist recruitment and fundraising. IS has been particularly successful in making the case that Islam is under siege by the West, and that the poverty and discrimination many Muslims encounter justify violent action. The harsh exigencies of life in suburbs of Paris and Brussels have more power to convince than do even the most rational pleas to renounce violence. Since the 9/11 attacks, the U.S. government has tried various counter-messaging themes and formats, but it remains unclear how successful these efforts have been. Until terrorism prevention campaigns address issues such as jobs and housing, terrorist groups will find plenty of recruits.

The tech giants must recognize the difficulty of establishing credibility (especially because they are American businesses) if they are to undermine the likes of Islamic State. The roots of terrorism run deeper than weak appeals for peace.

Philip Seib is a professor at the University of Southern California’s Annenberg School. His book, As Terrorism Evolves, will be published in October.