A firewall is a security device which can be either hardware and/or software based. The purpose of a firewall is to permit or deny proxy data coming in and out of your computer system and/or network. A firewall may simply be hardware deep packet inspection, or linked to various software signatures looking at anti-virus, anti-spam, or phishing threats. In this latter case they are often referred to as UTM devices (Unified Threat Management). If a higher degree of security is required, then a Next Generation Firewall (NGFW) should be considered.