On the eve of trial in January 2000, Microsoft settled a long-running antitrust and unfair-competition lawsuit brought by Caldera, which had acquired the rival operating system DR-DOS. Caldera alleged Microsoft used predatory tactics to crush DR-DOS, including the so-called 'AARD code' — hidden instructions in beta versions of Windows that displayed cryptic, non-fatal error messages when they detected DR-DOS instead of MS-DOS, designed to make the competitor look unreliable. The settlement terms were confidential, but Microsoft later disclosed a figure of roughly $155 million, with some outside estimates higher. The case is frequently cited as documentary evidence of the hardball tactics Microsoft used against competitors during Bill Gates's leadership.