A firewall is a network security system. It can be hardware and/or software based. Firewalls control incoming and outgoing network traffic by creating a barrier between a trusted network and one that is not, such as the internet. Firewalls have evolved since their introduction in the late 1980’s to be able to keep up with the constant threats of malware and hacking attempts. Today’s firewalls protect not only servers, but the applications running on them. Application-layer firewalls filter and block specific content or websites.