So the termination is likely to produce months or more of disadvantage to al-Shabab. Its ability to communicate with fans and generate a supportive social network certainly hasn't been eliminated, but it's been seriously and measurably damaged for a fairly significant length of time.
This isn't the only dataset suggesting that disruptions to online extremist networks do long-term damage. An ambitious New America Foundation paper published last week by Aaron Zelin, a fellow at the Washington Institute for Near East Policy, tracked the number of posts per day at the most important jihadi message forums.
Zelin also benefited from a found experiment when two of the three top forums he was tracking were knocked offline for a significant amount of time. The cause of the disruption is still unknown, but its effects were easy to see in Zelin's data.
While two of the three forums were offline, the third one picked up some activity -- but not nearly enough to compensate for the loss of other two. The overall number of posts per day plummeted by 80 percent. After the two disrupted forums returned, their posts per day ran 13 percent lower than before the takedown.
One reason the disruption was less severe on the forums than on Twitter has to do with the structure of each network. When al-Shabab's Twitter account was terminated, it lost all of its followers and had to rebuild from scratch. User accounts on the forums can be backed up, so users did not have to re-register and they could jump right back in.
The forums are also destination Web sites; you go there seeking out specific kinds of discussion and community. On Twitter, where attention spans are shorter, most users follow multiple accounts, so the loss of @HSMPress was more easily overlooked.
Importantly, although there's a Web forum devoted specifically to al-Shabab, it has never gained nearly the same kind of traction that the Arabic jihadist forums enjoy. Al-Shabab is much more reliant on social media than the broader global jihadist community, so the termination of its Twitter account was a pretty big deal.