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AVG Free Edition is a free antivirus and antispyware software for Windows

AVG Free edition offers for free :
Basic anti-rootkit protection, e-mail and instant messanging scanning, anti-spyware, phishing protection.
Also includes a update manager:

Please notice that AVG Anti-Virus Free Edition may only be used on one computer for personal use.
Also pay attention that in the AVG download page you can download by default the "AVG Download Manager" which is a 800 kb file that downloads the hole AVG application. If you want the actual download file then hit on the "Installation files" tab and then select the "AVG Free 9.0 for Windows" link (74 MB).