Signal's SMS registration codes expire after a few minutes, so you wouldn't even need to know the duration of the incident. Let's be conservative and say the codes expire after 5 minutes (it's probably shorter), then Signal is registering 380 devices a minute.
My reading of the post is that they determined the "1,900 users" figure by the number of users who had requested a code during the duration of the Twilio incident, as the attacker could have accessed their SMS messages at any point during the compromise:
> During the window when an attacker had access to Twilio’s customer support systems it was possible for them to attempt to register the phone numbers they accessed to another device using the SMS verification code. The attacker no longer has this access, and the attack has been shut down by Twilio.
At least number of requests + number of open unverified and unexpired requests. So you need to guess average length of time to verify and the abandon rate.
It also seems like there is also a buffer period when the numbers are registered and not yet purged from the twilio system:
> 1) their phone numbers were potentially revealed as being registered to a Signal account, or 2) the SMS verification code used to register with Signal was revealed.
We don't know how often Signal purges that, so, although unlikely, it could be a day or a week or more of registrations.
380 devices / minute would imply Signal is adding 547,200 users / day, or 199,728,000 users / year. That seems way too high. Granted some could be multiple devices per user, but still...
200M users/yr does not sound unrealistic to me given the network effects of Signal. I'm certainly not suggesting that's the actual rate - but I'd be willing to believe it's within an order of magnitude.
> Here's an article from last year mentioning 50M+ downloads in 10 days.
That was a period in which WhatsApp had just announced their new ToS, indicating that the data about their users was to be merged with Facebook's. Consequently, many users became aware of the enormous privacy issues with all Facebook/Meta products, and abandoned WhatsApp for other services, mostly Signal and Telegram.
I doubt that this period can be used to interpolate the Signal growth for the rest of the year, although the network effect has probably resulted in a much higher growth rate than before the WhatsApp exodus.
Edit: a Tweet from Elon Musk ("use Signal") most probably contributed a lot to that raise in awareness, and the one-time surge of increased growth for Signal.
