I have no idea, but Mike1's account was used, though I cannot confirm that his real name was MICHAEL NIMITSIL or not (as is noted in the comments on the Outside article).
There is a letter from the last guy who saw him here:
http://www.alpinismonline.com/alp-notas.asp?id=10198&lang=ENFor those interested, what MoT is referring to:
"Mike1" signed up for the forum a while ago and started discussing his plans for Aconcagua. Several climbers reacted to that on this thread:
http://7summits.com/forum/index.php/topic,1663 His last reply there was 1st November and as far as I can tell the next time his account logged in was 9th December, likely used to write the above message by his girlfriend.
In any case my condoleances to Michael Nimitsil's family
