Thank you both for your prompt responses.
Per the suggestion above, I sent [a copy of] the file to the User Files area of the Virus Vault, and e-mailed it to avast (which was effected by a manual update search).
Yes, I have the MBAM paid version... but the protection module is NOT enabled: I use MBAM purely as an on-demand scanner.
And yes, I believe the warning I received corresponds to the picture above, which you say was generated by the anti-rootkit scanner. However, for what it's worth, I was unable to duplicate the warning, neither by rebooting (and waiting 8+ minutes), nor by running an on-demand MBAM scan.