user510: In 2001, Nigel Short went public with the opinion that he had in fact played Bobby Fischer on the Internet Chess Club.
This was denied by Fischer himself, and the consensus seems to be that it was not in fact Fischer that he was playing. However, though I have the impression of reading something about who Short was really playing some time ago, I cannot remember this for sure and now cannot find a conclusive source on who Short's opponent actually was. Has there ever been a definitive statement on this?

user15649: Fischer never, ever denied it.  What he said was he doesn't play chess anymore, and when a reporter told him what Nigel said, he responded "He can say what he wants".  Not playing anymore means currently; that game happened prior to that interview, so it wouldn't be a lie.  The fact that he didn't outright say that Nigel was lying seems... A little Fischy to me.

user26072: Well, as of 2021 a much more concrete answer can be provided: https://www.reddit.com/r/UnresolvedMysteries/comments/mv0vz5/solving_the_fischer_chess_games_in_2001_gm_nigel/
In short (pun not intended): 'Fischer' was actually Deep Fritz using its second choice moves. (Apparently, every move played by 'Fischer' after the first few turns corresponded to Deep Fritz's second choice.) Another engine with high correspondence was Gambit Tiger.

user1791: If you can believe that Fischer would play as white:
1.f4 e5 2.f5 d5 3.g4 Qh4# White checkmated 0-1
Unlikely.  More likely it was someone with a chess engine having some fun, likely someone who is very inexperienced as provided by the example.  He would make very poor opening moves and let the chess engine take over beating many GM's. 

user47: Nobody knows who he played, because nobody has come forward to take credit; however, some chess sleuths compared the moves against various engines and found that there was considerable evidence to support a particular engine (I believe it was called "blitz tiger") as the mysterious Fischer.  Because of the incident where Short chatted with Fischer, there must have been a human behind the account as well (many accounts on the ICC are run entirely by computers without any human interaction at all).  The ICC can probably do some user profiling to figure out who the player is either by comparing the location/IP/e-mail to another user or by doing some internet forensics based on information they gathered from the incident.  However, it seems like they either don't care or if they did find out, they don't want to share (based on what xaisoft said) so it will probably always be a mystery.  And, to be honest, it's a better story that way, and because all this is is a good story, that's a good thing.

510: <p>In 2001, Nigel Short went public with the <a href="http://web.archive.org/web/20130630071150/http://www.bobby-fischer.net/Bobby_Fischer_Articles51.html" rel="noreferrer">opinion that he had in fact played Bobby Fischer on the Internet Chess Club</a>.</p>
<p>This was denied by Fischer himself, and the consensus seems to be that it was not in fact Fischer that he was playing. However, though I have the impression of reading something about who Short was really playing some time ago, I cannot remember this for sure and now cannot find a conclusive source on who Short's opponent actually was. Has there ever been a definitive statement on this?</p>
 15649: <p>Fischer never, ever denied it.  What he said was he doesn't play chess anymore, and when a reporter told him what Nigel said, <a href="https://www.youtube.com/watch?v=Um1Ji9MUqgo" rel="nofollow noreferrer">he responded</a> &quot;He can say what he wants&quot;.  Not playing anymore means currently; that game happened prior to that interview, so it wouldn't be a lie.  The fact that he didn't outright say that Nigel was lying seems... A little Fischy to me.</p>
 26072: <p>Well, as of 2021 a much more concrete answer can be provided: <a href="https://www.reddit.com/r/UnresolvedMysteries/comments/mv0vz5/solving_the_fischer_chess_games_in_2001_gm_nigel/" rel="noreferrer">https://www.reddit.com/r/UnresolvedMysteries/comments/mv0vz5/solving_the_fischer_chess_games_in_2001_gm_nigel/</a></p>
<p>In short (pun not intended): 'Fischer' was actually Deep Fritz using its second choice moves. (Apparently, every move played by 'Fischer' after the first few turns corresponded to Deep Fritz's second choice.) Another engine with high correspondence was Gambit Tiger.</p>
 1791: <p>If you can believe that Fischer would play as white:
1.f4 e5 2.f5 d5 3.g4 Qh4# White checkmated 0-1
Unlikely.  More likely it was someone with a chess engine having some fun, likely someone who is very inexperienced as provided by the example.  He would make very poor opening moves and let the chess engine take over beating many GM's. </p>
 47: <p>Nobody knows who he played, because nobody has come forward to take credit; however, some chess sleuths compared the moves against various engines and found that there was considerable evidence to support a particular engine (I believe it was called "blitz tiger") as the mysterious Fischer.  Because of the incident where Short chatted with Fischer, there must have been a human behind the account as well (many accounts on the ICC are run entirely by computers without any human interaction at all).  The ICC can probably do some user profiling to figure out who the player is either by comparing the location/IP/e-mail to another user or by doing some internet forensics based on information they gathered from the incident.  However, it seems like they either don't care or if they did find out, they don't want to share (based on what xaisoft said) so it will probably always be a mystery.  And, to be honest, it's a better story that way, and because all this is is a good story, that's a good thing.</p>
