Signaling processes or process groups can seriously affect the stability of
this application or other applications on the same system.

Accidentally setting an incorrect `PID` or `signal` or allowing untrusted
sources to assign arbitrary values to these parameters may result in a denial
of service.

Also, the system treats the signal differently if the destination `PID` is less
than or equal to 0. This different behavior may affect multiple processes with
the same (E)UID simultaneously if the call is left uncontrolled.