What do you call someone who accesses something? [closed]

For example, someone who accesses an IT system?

Edit: for clarity, I'm not assuming any intent or relationship. For example, not a "hacker" or "vandal" or "client". I'm looking for the most generic term. I had considered "accessor", which seems natural, but I did not see that in my dictionary lookup. I'm happy with that term, though, since it would be understandable to a reader even if not familiar.

Solution 1:

If it's a technical discussion about the act of performing the access itself, they're the accessor.

If it's a discussion about the system they're accessing, they might just be the client or user.