Speaking today at the Aspen Security Forum and with an eye on his demands for more surveillance powers and “back doors” in all commercial encryption software, FBI chief James Comey declared that ISIS is a bigger threat than al-Qaeda, and a huge domestic threat.

To back this up, Comey claimed ISIS has 21,000 English language followers on Twitter, and that conceivably a lot of those followers could be inside the United States, and subsequently might attack the US at some point in the future.

Comey has recently praised Twitter for its support for FBI investigations of Islamist communication, and reiterated his concerns about private communication today, saying he worries “very much about what I can’t see” and therefore needs to be able to see everything.

Comey went on to brag of FBI arrests of a “significant number” of people in the last eight weeks for being “radicalized,” though he offered no details on who all these people are and what, beyond Twitter, they were actually doing.