FormBook is an infostealer malware that was first discovered in 2016. It steals various types of data from infected systems, including credentials cached in web browsers, screenshots and keystrokes. It also has the ability to act as a downloader, allowing it to download and execute additional malicious files. It operates on a Malware as a Service (MaaS) model, where cybercriminals can purchase access to the malware for a relatively low price.