This letter in Nature Biotechnology reports the discovery that a piece of code frequently used in database sequencing has an error---which has been there for 15 years. According to the authors, "Obviously, minor errors in research, and particularly in software source code, are quite common. This case is noteworthy for three reasons: first, the BLOSUM matrices are ubiquitous in computational biology; second, these errors have gone unnoticed for 15 years; and third, the 'incorrect' matrices perform better than the 'intended' matrices." (From Neil Saunders, via Titus Brown.)