A software bug is a fault in software. Most bugs arise from mistakes and errors made by people in either a program's source code or its design, and a few are caused by compilers producing incorrect code. Locating bugs (via a code review) is something of an art. It is not uncommon for a bug in one section of a program to cause failures in a completely different section, thus making it especially difficult to track. Large software programs are unlikely to ever be totally bug free and it’s common for software to be released with known bugs.