Signature scanning and algorithmic detection

Definition
Signature scanning and algorithmic detection (also known as scanners) are a common class of anti-virus tools.

"They are static analysis detection tools (i.e., they help detect the presence of a virus). Scanners also perform a more limited role as identification tools (i.e., they help determine the specific virus detected). They are primarily used to detect if an executable contains virus code, but they can also be used to detect resident viruses by scanning memory instead of executables."

Overview
"They may be employed proactively or reactively. Proactive application of scanners is achieved by scanning all executables introduced to the system. Reactive application requires scanning the system at regular intervals (e.g., weekly or monthly)."