Arakyd Viper Droids, also known as Probe Droids, were the biggest success in Arakyd's Probot line. It had a blaster and a self-destruct. It's purpose was to search for Rebel base in the Galaxy, one of these found the Rebel base on the planet Hoth and informed Darth Vader of the existence of the base. Lego has only made one, and included it in the 2007 set Hoth Rebel Base.
There are three variations of Probe droids: