Avast! (styled avast!) is an antivirus computer program developed by AVAST Software a.s. (formerly known as ALWIL Software a.s.), a company headquartered in Prague, Czech Republic, with offices in Linz, Austria; Friedrichshafen, Germany; and San Mateo, California. The name Avast is an acronym of "Anti-Virus – Advanced Set". The official, and current logo of Avast! is a white orb with the letter 'a' on it and an orange circle around it, sticking out to four directions.

Avast! Antivirus software is based on a central scanning engine that is certified by ICSA Labs and West Coast Labs' Checkmark process. Avast! also offers anti-spyware technology, also certified by West Coast Labs' Checkmark process, as well as anti-rootkit and self-protection capabilities.

Virus Bulletin has multiple times awarded Avast! Antivirus with its VB100 Award for 100% detection of "in-the-wild" viruses, and also won the Secure Computing Readers' Trust Award.

Avast! Free Antivirus is the freeware version of the Avast! antivirus software available to Microsoft Windows, Mac OS X and Linux users, while Avast! Pro Antivirus is offered to businesses and users who want additional features. Priority updates are delivered automatically using PUSH update technology in Avast! Pro Antivirus. Avast! Pro Antivirus also has a command line scanner and a script blocker; however, as of version 6, the script blocker is available also to users of the free version.

Read more about Avast!:  History, Features, Versions, *5.1, *5.0, Awards and Certifications