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/
Heh, reminds me of my national counting system where "halv seks" would mean 5,5. Aka. half before six, and not half of six. :P