Free Antivirus programs:1. Avast Home Edition Free Antivirushttp://www.avast.com/eng/avast_4_home.htmlI have to crown Avast as the overall best free antivirus for, among other reasons, having excellent virus and spyware detection rates according to antivirus test results from AV-Test.org.
Avast antivirus manages to provide a simple and functional user interface, while also being very customizable and feature complete. The active protection feature monitors seven different ways that a virus could enter your computer, including Web browsing, email, file sharing, and more.
Avast also features scanning on boot up if you choose to do so. That's something you don't want to do on every boot as it takes quite a while. However, if you suspect you have been exposed to a virus or spyware it is the best way to detect and remove active infections.
2. Avira Personal Free Antivirushttp://www.free-av.com/en/download/1/download_avira_antivir_personal__free_antivirus.htmlAvira is another one of the best free antivirus products, but it is not as full featured as Avast. The free version of Avira doesn't claim to protect against spyware, but I believe there is some crossover between what is defined as a virus and as spyware. If you want to make sure you are covered for spyware you can use something like SuperAntiSpyware which also has a free version.
Avira has an attractive interface, but it needed more tweaking to get things to function the way I wanted than did Avast. According to AV-Test.org Avira rates slightly higher than Avast for virus detection. However, if the spyware tests were run on the free version of Avira the score would be very low since they reserve the antispyware feature for the paid version.
3. AVG Antivirus Free Editionhttp://free.avg.com/download-avg-anti-virus-free-editionAVG is the most popular and one of the best free antivirus software products. AVG has a very polished user interface and is easy and comfortable to use. AVG detects both viruses and spyware in the free edition. However, in the test mentioned above the detection rate is a little lower than Avast or Avira.
The main thing that puts AVG last in my choices for best free antivirus is the amount of functionality left out of the free version verses the the paid version of the software. You still get good basic protection, but Avast and Avari cover more of the infection pathways than does AVG.
All three of these best free antivirus choices can be easily installed and uninstalled. You can feel free to try all of them to choose your favorite.
If the problem won't allow you access to the internet try the following:you could (on another machine) download & burn/save to CD "Stinger" from link below. I believe Stinger hits about 400 of the most currently common & nasty Viruses & Trojans.
It's BIG advantage is that it doesn't have to be installed nor need updates.
You simply place it in you CD/DVD drive and from desktop click to open My Computer then click to open & run the D: or E: or ? drive the CD is in. It runs as an application without install.
Personally, when downloading & saving Stinger, I re-name it at the "save as" screen to anything else to prevent malware from recognizing it (i.e.: "beehive.exe"). Hope this helps get you back to using other means for follow-up. Good Luck!!
http://vil.nai.com/vil/stinger/