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xkcd #3314: Vulnerability
(lemmy.nz)
Title text:
Other numbers are largely unaffected, but anyone using '4' for their certificate key is urged to upgrade to '5'.
Transcript:
Transcript will show once it’s been added to explainxkcd.com
Source: https://xkcd.com/3314/
So that’s why Duolingo hides numbers from us! (And probably also why Danish people switch to English or German no matter if you start in Danish or not..)