Here's some links to articles about cheating in chess. The first article by IM Tim Harding is very long and detailed, and well worth reading - if you're interested in this topic. And while we're on the subject of cheating let's not forget a famous, well more accurately infamous GM well known not only for his lack of chess etiquette but lack of chess ethics as well:
Milan Matulović (born 10 June 1935) is a chess Grandmaster who was the second or third strongest Yugoslavplayer for much of the 1960s and 1970s behind Svetozar Gligorić and possibly Borislav Ivkov. He was primarily active before 1977, but has remained an occasional tournament competitor as recently as 2006. During his career he was accused of "throwing" games in return for cash bribes to enable his opponents to make an IM or GM norm
Over the board he was known for playing out hopeless positions long after grandmaster etiquette called for resignation, allegedly in the hopes of reaching adjournment (suspension of a game for resumption the next day, common in tournament play at the time) so that the news reports would read "Matulović's game is adjourned" rather than "Matulović lost!"
Perhaps Matulović's most notorious transgression was against István Bilek at the Sousse Interzonal in 1967. He played a losing move but then took it back after saying "j'adoube" ("I adjust" – spoken before adjusting pieces on their square, see touch-move rule). His opponent complained to the arbiter but the move was allowed to stand. This incident earned Matulović the nickname "J'adoubovic". This reportedly happened several times, including in a game against Bobby Fischer.
More seriously, in the aftermath of the 1970 Interzonal tournament at Palma de Mallorca, he was accused of "throwing" his game against Mark Taimanov in return for a $400 bribe, thus allowing Taimanov to advance to the Candidates matches,where he was famously defeated by Bobby Fischer 6–0. The accusations centered on Matulović's conduct during the game and the alleged feebleness of his resistance. The score of the notorious Taimanov–Matulović game follows, from which the reader can draw his or her own conclusions:
SOURCE (and citations): https://en.wikipedia.org/wiki/Milan_Matulovi%C4%87
PS: Here's a June 19, 2013 update on accused cheater Borislav Ivanov along with links to several previous articles about him