Online Armor Personal Firewall is a firewall developed by Tall Emu Pty Ltd that provides protection on a Microsoft Windows operating system from both inbound and outbound attacks. It comes in both free-for-personal-use and commercial versions. Though compatible with only Windows NT, 2000, and XP, the possibility of creating a version compatible with Vista is being investigated. The freeware version has somewhat limited features compared to marketed versions. Most notably, it lacks the ability to update the software or definitions. Thus, product upgrades must be manually downloaded from its website.