[Update: MSN has removed Backgammon from its games. Probably because of the rampant cheating. For a more fair place to play Backgammon that minimizes the chance of cheating (particularly because of the availability of instant replays) try https://www.gameslush.com/backgammon]

Figured I’d compile this list after seeing several cheaters that exploit the “repeated-undo stall/timeout” bug. Hopefully this list will help legitimate players safely quit the game before entering a match with these sociopaths. Don’t know why these cheaters spend so much time on such fruitless (and mindless) idiocy when they could instead devote their efforts to learning how to play properly. It becomes obviously fishy when these players rated 2000 and higher play so poorly … you can smell the undo-stall cheat coming from a mile.

Here’s the list so far and I’ll update it as it grows:

nabnabnab8
Long_TeaBagger
rollierocket
OP91
Tricked_Safe1
yambag7
PerfectBalance5
SlowerLeech
BestInTheWest67
Deadly_Timing
Monteceito
StainableMetal
Master_of_Dice
quickie1913
SteadierPig6
OBX_7
TempFormula6
Emilian11

2015-01-07: WirierCloth

More as of 2014-07-31:
opticstwo
prancing_horse2
GogglesPaisano5

More as of 2014-06-13:
EnamoretedAunt
HitByABus
Length_Axis

More courtesy of the Microsoft community forums thread:
Ciscoman9
filini
smuglight
future_seer
sprite
Elephant__
LolaBadGirl
George1772
Guest (with 23,000+ games)
Guest (with 10,000+ games)
RiskQueen

Edit — thanks to Bob_Who for the following update:

Novy22
CrazyFastTD
TutorialCoder
Tigermartin7890
Sieeeeeeeb
MD_Danny
Tradable_Toast
ErrantMarlin
eastcoast_poker
Burdened_Steet
PADDLES__
Peak_Wizard0
Gammon4all
Eqlant
BobbyJ30
PSstarman1
Barmy_Quotient

Courtesy of this video (link):
CulichiGuapo

Prior to 2012-10-14:
Stereo_Chart
NathDan0615
Cursive_Tiger
BCCFMPTN
hunter_gunter