Additional Real Time Protection:
ThreatFire 4.1 [Behavior Blocker](Free) -
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ThreatFire continually protects your PC against attacks by detecting malicious behavior, such as capturing your keystrokes or stealing your data, instead of only looking for known threats like normal antivirus software. By implementing sophisticated real-time behavioral analysis ThreatFire is able to stop never- before-seen "zero-day" threats solely by detecting their malicious activity.
Additional on-demand scanner:
Hitman Pro (Trial) -
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An on-demand scanner using multiple anti-malware engines and cloud technology. It offers unlimited free scanning but once you use it to remove detected malware it switches to a 30-day trial version. I recommend using it after you've scanned your hard-drive with the other products you have installed.
Additional browser protection:
WOT (Free) -
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To help you avoid malicious sites you can use Web of Trust (WOT) a website rating browser plugin. After you add it to your browser make sure you only visit websites rated "Green" by WOT
VTzilla (Free) -
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VTzilla is a Mozilla Firefox browser plugin that simplifies the process of scanning Internet resources with VirusTotal. It allows you to download files directly with VirusTotal's web application prior to storing them in your PC. Moreover, it will not only scan files, but also URLs.
The scanning options are embedded in Firefox's context menu and download dialog, making the analysis process as easy as clicking a single button.
More Info
Additional browser plugins
Adblock Plus (Free) -
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Adblock is a content-filtering extension for Mozilla Firefox- and Mozilla Application Suite-based web browsers. Adblock allows users to prevent page elements, such as advertisements, from being downloaded and displayed.