What does this mean and what should I do?

Exactly what version of Mojave is installed. It should be 10.14.6 and all Security Updates should also be installed. There may or may not have been some Boot ROM updates included in newer updates to Mojave and could potentially remove this eficheck.dump issue.

If all above have been applied -

Suggest downloading from a Trusted Developer and Respected ASC Contributor the application Malwarebytes for Mac. It is free or paid for added features. Run the Application and it should remove the malware / adware. Once done, restart computer and test.

There are no known Viruses in the wild that self replicate and affect macOS. There are Malware and Adware that does affect macOS and are often times downloaded as part of an Application from Third Party UnTrusted Site and get installed along with the Application.

Welcome and Thank you too ;-)

Somewhere is Mojave - Apple Introduced an Check EFI as part of the Hardening of the OS and Boot Rom to guard against Tampering with very low level processes from being Altered or modified by UnAuthorized actions or Software.

As we have seen subsequently in Catalina - the System Files have been further Hardened by creating a New Volume one for User Data and one for the system Data. The System Data is a Read Only Volume. Apple has gone a step further in Big Sur and Hardened the System Volume into a Read Only Volume and Sealed Volume.

We do not test know what the Monterey macOS to come later this year will be like.

All the above is intended to explain the lengths to which Apple is attempting to keep the Boot ROMs and whole system out of the hands of UnAuthorized actions and software.

Are you currently running any third-party anti-virus packages or so-called "cleaning" apps? They are the leading cause of performance issues in Macs.

MalwareBytes is the sole exception. It excels at finding adware picked up from unscrupulous download hosting sites. Did you run it as P. Phillips has suggested?

I do have CleanmyMacX - Number One get it off the Computer as per the Developers Instructions. Are there any AntiVirus, Disk Cleaner, Optimizers, Un-installers, etc installed which should be removed as per Developers Instructions. They are useless, unneeded, cause havoc and interfere with the normal operation of the OS and may even Corrupt the OS requiring a Reinstallation. 

Any Third Party Applications that will interfere with the normal operation of the OS, alter, modify, remove or delete or attempt to do so is an invitation for disaster and may require a Reinstallation of the OS.

This computer OS is seriously compromised and may require as Re=Installation