Avira 10 has now been reported as an ad-supported program including a toolbar that requires you change your search provider to ASK.com. If you do not like advertising popups appearing on your screen, please consider a different free antivirus program. Microsoft Security Essentials is one suggestion as it covers spyware also.
I was fairly impressed with this piece of software. For a free version it loads very fast when the computer boots, especially when compared to bloated paid programs (choose any mainstream security suite). I don't know how effective this program is but it should be comparable to other free antivirus programs out there such as AVG Free or avast! Home Free.
From Avira :
Avira AntiVir Personal Free Antivirus is a comprehensive, easy to use antivirus program, designed to offer reliable free of charge virus protection to home-users only. Avira offers: Extensive Malware Recognition of viruses, Trojans, backdoor programs, worms; Automatic incremental updates of antivirus signatures, engine and entire software; Permanent virus protection, with Virus Guard real time monitoring; Install and configuration in just a couple of steps, setup to protect your PC in minutes; Virus protection against known and unknown threats, using an advanced heuristic system; Scheduler where you can set the scanner to make automatic virus scans or updates on your system; Forum and phone support; Knowledge Base with virus descriptions available on web site; Rootkit Detection and Removal; A modularized AV-search engine for improved scan performance.
Version 9 introduces a quick-removal button for eliminating viruses with a single click, enhanced anti-spyware and anti-adware engines, and support for low resolution netbook screens.