aVast!Antivirus
avast! antivirus software provides complete virus protection for your computer. Antivirus engine is complemented by anti-spyware, firewall and antispam modules to protect you against phishing schemes, identity theft and internet-distributed web viruses. Automatic updates for greater user convenience and safety. Top user ratings among free antivirus software.

CCleaner
CCleaner is a freeware system optimization, privacy and cleaning tool. It removes unused files from your system - allowing Windows to run faster and freeing up valuable hard disk space. It also cleans traces of your online activities such as your Internet history. Additionally it contains a fully featured registry cleaner.

RegCure
RegCure enables you to fix your PC's windows registry in the way that is most comfortable for you.  Clean your registry manually according to your own specifications or perform a thorough scan and clean it automatically!.

Spybot S&D
Spybot - Search & Destroy detects and removes spyware, a relatively new kind of threat not yet covered by common anti-virus applications. Spyware silently tracks your surfing behaviour to create a marketing profile for you that is transmitted without your knowledge to the compilers and sold to advertising companies.