One of the longest-running cheating scandals happened during what's sometimes called "Baseball's Steroid Era." From the late '80s to the late 2000s, countless players used steroids to improve their speed, stamina, and accuracy. It's hard to pin a number on this scandal, because until 1991, steroids were not banned in baseball, and there was no systematic testing until 2003 [source: ESPN].
Among the players tainted by the Major League Baseball (MLB) doping scandal were Mark McGwire, Sammy Sosa and Barry Bonds. All three set home run records, and all three used steroids to enhance their games. In 1998, McGwire broke Roger Maris' 1961 record of most home runs in one season (61) with 70 runs. Sosa finished second with 66 -- hitting 26 more than he did the year before. Bonds hit 73 homers in 2001 even though he'd never reached 50 in previous seasons [source: ESPN].
There were suspicions and investigations in the early 2000s, and in 2005 the U.S. House of Representatives Committee on Government Reform held hearings on steroid use after player Jose Canseco released his tell-all book about doping in baseball [source: ESPN]. Under subpoena in the 2005 hearings, McGwire denied his steroid and human growth hormone use; in early 2010, he finally confessed [source: ESPN]. Sosa also denied using drugs in those 2005 hearings but was later linked to a positive test.
In one of those early investigations, the Bay Area Laboratory Collective (BALCO) was investigated by federal agents; Bonds said he did take substances they supplied to his trainer, but he thought they were linseed oil and rubbing balm [source: ESPN]. He passed the drug test at that time, so the investigation on him ceased. In 2007, Bonds was found guilty of obstruction of justice for lying under oath during those investigations [source: ESPN].
In 2007, MLB's Mitchell Commission (headed by former Sen. George Mitchell) issued a report linking 89 major leaguers to performance-enhancing illegal drugs.