Security is the top priority nowadays and the very popular antivirus program proves that this does not always have to be associated with high costs Avira AntiVir Personal - Free Antivirus

Avira AntiVir Personal 10 - Free Antivirus
The free virus protection with an integrated real-time scanner.

AntiVir watches in the background and, as a comprehensive and flexible tool, reliably protects the system against viruses, malware, unwanted programs and other dangers in real time.
Manual scanning of downloads, directories or hard drives with the “file checker” is also possible.

Daily virus signature updates keep the program up to date.
Shorter intervals are reserved for the paid premium version.

System Requirements

• Computer from Pentium, at least 266 MHz
• Operating system
  - Windows 2000, SP4 and Update Rollup 1 or
  - Windows XP, SP2 (32 or 64 bit) or
  - Windows Vista (32 or 64 bit, SP 1 recommended)
  - Windows 7 (32 or 64 bit)
• At least 150 MB free space on the hard disk (when using the
  Quarantine and more for temporary storage)
• At least 256 MB RAM under Windows 2000 / XP
• At least 1024 MB RAM under Windows Vista, Windows 7
• For the installation of Avira AntiVir Personal: Administrator rights
• For all installations: Windows Internet Explorer 6.0 or higher

Deliverables

• Control center for monitoring, administration and control of the entire program
• Central configuration with user-friendly standard and expert configuration and context-sensitive help
• Scanner (on-demand scan) with profile-controlled and configurable search for all known types of viruses and malware
• Integration into Windows Vista User Account Control to be able to perform tasks for which administrative rights are required
• Guard (On-Access Scan) for constant monitoring of all file accesses
• Integrated quarantine management for isolating and handling suspicious files
• Rootkit protection to find malware that has been installed hidden in the system of the computer (so-called rootkits) (not available under Windows XP 64-bit)
• Direct access to detailed information on viruses and malware found via the Internet
• Simple and quick update of the program, virus definitions (VDF) and search engine through single file update and incremental VDF update via a web server on the Internet
• Integrated planner for planning one-off or recurring tasks such as updates or test runs
• Extremely high virus and malware detection through innovative search technologies (search engine) including heuristic search processes
• Detection of all common archive types including detection of nested archives and smart extension detection
• High performance thanks to multithreading capability (simultaneous scanning of many files at high speed)

Note:
To keep it up-to-date, the download refers to the manufacturer's website