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This guide will present a number of free and effective measures to help protect your windows Xp/Vista pc against an ever-increasing number of viruses, trojans, spywares, malwares and worms;

1. Get a good antivirus, for this, I would recommend Avira Antivir, this is free, and Pc Pro achieved a great rating from Pc Pro, this is lightweight, but a great alternative to the far heavier (and more expensive) Norton and Kaspersky.
2. Keep your system updated! Particularly windows Vista users, but it is important that your system is kept up-to-date, either by enabling auto-updates, or updating the system yourself.
3. Replace the default firewall. Although a vast improvement on XP, the Window’s Vista default firewall has better alternatives that are nonetheless free, for example, Comodo Firewall Pro, with compatibility back to Windows 2000. The free version of ZoneAlarm is also good, but I have found that to often be too intrusive compared to Comodo. Windows firewalls, because they are the default with all window.
4. Get both of the following programs; Spybot Search and Destroy, and Lavasoft’s Ad-Aware 2007, both of which are free (although there is a premium version of Ad-aware available), both of these are excellent at routing out spyware and malware, and although Spybot SnD is the more powerful tool, Ad-Aware is more user-intuitive, and both search for spyware in different locations.
5. Scan your system regularly, at least once a week, scanning for viruses and malware separately, and, if this takes a long time, try defragmenting your hard-disks, as this should dramatically decrease the scan time of your system.
6. Keep all your files backed up, and ensure these backups still work, either by doing this manually, or creating an ISO image of your files and burning that to a disk.