Unknown Attack 1.0 could be downloaded from the developer's website when we last checked. We cannot confirm if there is a free download of this software available. The most popular version among the software users is 1.0. The program lies within Games, more precisely Action. We recommend checking the downloaded files with any free antivirus. This free program was originally developed by Falco Software, Inc. Game.exe or UnknownAttack.exe are the default file names to indicate the Unknown Attack installer.
From the developer:
Unknown Attack is a game about protecting the territory of your artillery base from unidentified attackers. As you progress, the pressure will grow as new species of invaders come at you. However, Allied boats, weapons and improvement bonuses will help you. The main task is to hold out against all enemy attacks as long as possible.
You may want to check out more software, such as Unknown Horizons, Beyond the Unknown: A Matter of Time Collector's Edition or Unknown Device Identifier, which might be related to Unknown Attack.