/usr/lib/mon/alert.d/aim.alert is in mon-contrib 1.0+dfsg-1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/mon/alert.d/../../mon-contrib/alert.d/aim.alert
/usr/lib/mon/alert.d/../../mon-contrib/alert.d/aim.alert