The computer security market is flooded with antivirus software that work but don't come cheap.

While viruses remain a threat to our precious data, you need not necessarily invest in expensive antivirus scanners - there are plenty of free options available that may give even some commercial vendors a run for their money.

We look at some of the best software available today for keeping your computer free of viruses and other malware. Later we help you decide the one most suitable for you.

Free Online Virus Scanners [run inside the web browser to scan your hard drive]

Trend Micro HouseCall - An online virus scanner that's absolutely free and scans your PC hard drive for any sort of viruses or even spyware. HouseCall allows you to remove detected infections. Works with Firefox and IE. Requires Java.

McAfee Freescan - This free virus scanner from McAfee is based on the McAfee VirusScan engine. Should viruses be found, FreeScan prepares a list of infected files and links to information about the viruses on your computer. It also gives you an option to clean your system. Requires IE with ActiveX.

Windows Live OneCare Scanner - A free antivirus online scanner from Microsoft that cleans your system from viruses and also recommends ways to improve the overall performance. Part of Windows Onecare.

Symantec Internet Security - An online virus scanner from the developers of Norton Antivirus 2007 can detect most virus threat but there is no option to delete the virus infected file or repair it. Does not examine compressed files. Requires IE with ActiveX.

BitDefender Online Scanner - Their Free Online Virus Scanner version 8 scans your system's memory, all files, folders and drives' boot sectors - the default options automatically cleans the infected files. Requires IE with ActiveX.

Free Anti Virus Software for Windows [Requires Installation]

Avast! Home Edition - One of the most popular antivirus software, can also be run from Explorer context menu. You can either scan the entire hard drive or selected folders. Ships with an Antivirus screen-saver.

AOL Active Virus - a free virus scanner from AOL based on Kaspersky Antivirus that doesn't require an AOL account to download the software. The software can be configure to check only new and modified files thereby reducing the memory requirements. Also support scanning of incoming and outgoing email messages.

ClamWin Virus Scanner - An opensource antivirus software that is great for running routine antivirus checks on your PC. You need to manually scan a file in order to detect a virus or spyware.

AVG 7.5 Free Antivirus - One of most popular free virus scanning software is AVG 7.5 Free Edition (read comments). Initially, there was confusion whether AVG 7.5 would be free like AVG 7.1 but the good news is that AVG 7.5 Free edition is already available for non-commercial, single home computer use.

Conclusion: Which one should I choose ?

Unlike Desktop antivirus software, online virus scanners do not proactively protect your PC against new virus infections.

But if viruses have already entered your hard drive and taken control of your existing desktop scanner program, any of the above listed online virus-scanning services can save your day.

If you are a fairly experienced web user who doesn't need an antivirus software to run in the background 24 hours, scan you drive at regular intervals using HouseCall. Others may install the AOL antivirus software which uses the Kaspersky virus definitions database.

Related: How to Trick the GMail Virus Scanner