This is the software publisher's description.

Security must not be a privilege. Under this motto, Emsi Software provides the Malware scanner a-squared Free completely free of charge for private use. But it is not a very limited version, it is a full tool to clean your computer from Malware. Not only Spywares, as detected by classic Anti-Spyware programs, but also especially Trojans, Backdoors, Worms, Dialers, Keyloggers and a lot of other destructive pests, which makes it dangerous to surf the web.

Trojans and Backdoors provide strangers with access to your PC. Once a Backdoor is installed, an attacker can take full control of your computer. A Trojan is best described as a piece of software pretending to be something it is not - they often contain Backdoors, and usually arrive as email attachments. A Keylogger is a type of Malware that invisibly records all keyboard activity, whereas Rootkits hide on your PC and manipulate internal system operations. a-squared Free specializes in recognizing and eliminating these types of Malware.

Your personal data and information is worth a great deal of money to certain advertising companies. They have no qualms about smuggling software into your system, recording information and spying on everything you do. Adverts that change the start page of your browser also belong in the Spyware/Adware category. a-squared Free completely removes Spyware from your PC. Traces of Spyware in the Registry and Tracking Cookies are also recognized.

This is the new v4 which now contains both anti-virus and anti-spyware modules, amongst other new features.