"hppostprocessing.bundle will damage your computer" -- cannot print anything

Hardware
7

Statement by HP:

We unintentionally revoked credentials on some older versions of Mac drivers. This caused a temporary disruption for those customers and we are working with Apple to restore the drivers. In the meantime, we recommend users experiencing this problem to uninstall the HP driver and use the native AirPrint driver to print to their printer.

More at: If you suddenly can't print to your HP Printer from your Mac, you're not alone: Code security cert snafu blamed • The Register

This particular issue is due to this revocation snafu like @dsh1705 has hinted. So, no real malware incident in this case.

According to this tweet, Apple already has pushed an update in order to stop macOS protecting their users against HP’s revocation saga:

https://twitter.com/stuartjash/status/1319765909234352128

According to Eclecticlight.co:

Update: The previously revoked signature has now been unrevoked, as of the night of 24-25 October. Thanks to Mr Macintosh for spotting this. Your old HP printer software should now work correctly again.
(0750 UTC 25 October 2020)

P.S. Regarding “uninstall the HP driver and use the native AirPrint driver to print to their printer” - that is how my HP printer is being set up for years. My HP printer is printing all along via AirPrint.