Multiple realities
(covers information from several alternate timelines)

Ensign Hayes served on the USS Enterprise-D in the 2370s.

In one of the quantum realities seen by Worf, Ensign Hayes responded from main engineering when the Enterprise-D received damage due to a Cardassian attack. He informed Captain William T. Riker that Commander La Forge was brought to sickbay due to plasma burns. (TNG: "Parallels")

He was at tactical when Lursa and B'Etor's Bird-of-Prey decloaked in front of the Enterprise-D at the Amargosa observatory.

Hayes was later on duty on the bridge and witnessed Data singing at his operations station. He also took a station during the Duras' attack on the Enterprise-D and was present when the Duras' ship was destroyed by a photon torpedo. (Star Trek Generations)

Ensign Hayes was played by Michael Mack in "Generations" and voiced by an unknown actor in "Parallels".
It is uncertain whether or not this was the same individual, as the Hayes in the parallel universe could have been assigned to engineering rather than security. The Star Trek Encyclopedia (3rd ed., p. 186) claims they are the same person.
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