I wrote:
Microsoft released a new version of Exchange Server at the start of the new year, which promptly caused everybody’s on-premises servers to crash.
The reason? The version number.
According to Microsoft’s blog post, linked from this report <https://www.theregister.com/2022/01/03/exchange_servery2k22_flaw/>, the version number concerned is not that of the server software, but of the antivirus signature file.
They released a PowerShell script to automate the fix, but it might not work properly, so there is an option for a manual fix as well.
Seems the fix is far from simple: Microsoft’s post about the bug and how to address it was updated seven times between publication on January 1st and the time this story was posted. Chatter in Microsoft forums and elsewhere suggests that the fix can be tricky to apply, and sometimes fails.