Ninja Editor
Seen on Message Boards and blogs and the like, the Ninja Editor is the type of person who makes a post, then almost immediately goes back to and then edits it quickly and without comment—like a Ninja.
This is usually innocent (like fixing typos, in which case it's customary to add something like "Ninja-edited for typo" just for clarity) but can also be used as flamebait, when a Ninja Editor's edit radically changes the content of the post. This can lead to an even more confusing situation where the earlier replies to a Ninja Edited post are replies to the original unedited post and later replies are replies to the new, edited post.
In the case of a total-post change, it may be deliberate trolling in order to bring about maximum confusion, or may be a newbie recanting after inadvertently running afoul of Internet Backdraft, in which case it may be extremely difficult for late-comers to the thread in question to figure out what exactly went the hell on in the first place. A more malicious application might be to ask a question, then once a few replies have been posted, edit the original post so that the answers now appear to be incriminating (ie- getting anyone to respond with a number under 13, then changing the question to "How old are you", resulting in an immediate ban under minimum age rules. This is why GameFAQs didn't allow editing for a long time, and while it is now allowed the above actions will get you banned.)
This can get really, really annoying in certain communities (especially Livejournal) where you can now edit comments, as most people have settings that email the comments to them, so in the space of a few minutes you can have half a dozen of practically the same comment clogging up your inbox.
People that are afraid of this happening to a significant comment may quote them so that it's part of their quote. This ignores that quotes can also be altered. (Usually just by moderators, however.)
This is the reason that some fora allow editing of articles only up to a certain time limit (let's say, one hour) after the post was made. Others only allowed editing until someone responds to the comment. More than a few popular web forum packages will, after a certain arbitrary boundary is passed (after X minutes, Y edits, edits after another user has posted, or in some cases the very first edit, no matter what) mention, in smaller text, that the post has been edited. And once they do this, they will start storing the old revisions of the edits too, visible only to the person who made the post and to moderators so that issues like the aformentioned GAMEFAQs one can be fixed.
A somewhat related phenomenon is the Ninja Post, where during the time an entirely new message is being written, one or more other corespondents will submit messages into the conversation where the aforementioned one was intended to go. In this case, specific references to location or primacy (eg.: “Like the last post says…”, “I'm surprised nobody's mentioned…”) will be rendered confusing or misleading.
See also Serial Tweaker. Contrast with Internet Detective.
...Ninja'd!