Unable to activate Modsecurity with Atomic Standard rules: modsecurity_ctl failed: Atomic Updater Modified (AUM) Installer (v6.0.0)

Symptoms

Unable to activate Modsecurity with Atomic Standard rules in Tools and Settings > Web Application Firewall:

modsecurity_ctl failed: Atomic Updater Modified (AUM) Installer (v6.0.0)
...
Package 1:aum-5.0-18024.el7.art.x86_64 already installed and latest version
Nothing to do
To complete installation run:
aum configure
and to update your rules:
aum upgrade

Cause

A temporary issue on the Atomic side.

Resolution

Wait until Atomic fixes the issue or:

1. Log into Plesk
2. Activate Modsecurity with Comodo rules in Tools and Settings > Web Application Firewall.