Malware
Just received the following message on my iMac.
iMac 27″, macOS 10.13
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Yes it is not malware, people are having a raft of problems with HP and their macs since yesterday,
looks like a code signing certificate has expired making printers and scanners inoperable.
On my macOS Mojave my HP printer is still printing, but the scanner has stopped functioning.
On another mac running macOS Sierra it prints and scans using the same software.
Looks like you will have to contact HP for advice.