Have you considered who might be sharing your computer's functionality?  I do not mean sharing with members of your family or colleagues but those individuals with whom you are not acquainted.  The presence of these unwanted visitors is a clear indication that your system has become infected by spyware that can include Trojans, keyloggers, adware, system monitors and cookies.

While these items can have the effect of causing system slow down, they also have a more insidious purpose.  Once your system has been infected by such code then your sensitive personal data or a log of your Internet activity could be winging its way to unscrupulous individuals to do with what they wish.  Keeping your system clear and safe from such infiltration is the designated task of Webroot's Spy Sweeper AntiVirus with AntiSpyware software which is now up to version 5.5. 

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In order to ensure you have the latest code available, Spy Sweeper will offer to check online for any product and definition updates prior to the actual installation taking place.  In my case this download consisted of around 17MB of data.  After entering a product serial number and agreeing to a system restart, Spy Sweeper gives you the option to register online before presenting its main interface.

As an initial procedure you would be advised to opt for a sweep of your system in order to detect any unwanted items that might already be present.  I was surprised to note that the actual scan dealt first with executable and data files found on various drives before rescanning the drives to check of archive files (Zip and Cab). 

By default this sweep will include all attached drives, including USB and flash units, plus memory.  As a result this process can be rather time consuming.  With around 132GB of data to check on the test system, the initial scan took 70 minutes and discovered 46 possible items that might need further action which could include placing possible infestations in quarantine.  By taking the quarantine route, rather than immediate removal, you can check to see whether the removal of such items might affect the running of other software that relies on the presence of associated code.

Following the initial scan, Spy Sweeper monitors your system for any attempts to infiltrate unwanted code,  Various shields, 13 in total, can be activated to cover specific areas. A tabbed interface lets you cherry pick from shields that have been categorised as Web Browser, Network, Windows System, Startup and Email Attachments.  You can also select which drives will be targeted by Spy Sweeper when conducting scans.

Spy Sweeper features a full set of customisation options.  Along with selecting the various shields and drives, you can chose from a full, quick or custom scan carried out on a user-defined schedule.  The anti-virus module, which is a licensed version of the well-respected Sophos software (better known in the business sector rather than the home consumer market), allows you to select from degrees of protection that are designated as full, partial or vulnerable.

Once set up to suit your individual circumstances, Spy Sweeper will provide real-time protection from a range of attempts to infiltrate your system.  Generally Spy Sweeper's presence will be kept to a minimum although I did detect a slightly longer delay when instigating an Internet connection with the Webroot software active.  System requirements are a 300MHz processor with 100MB hard disk and 256MB of RAM running Windows 2000 or later.  A one-year user license will cost £39.95 with a three-user licence being available for £49.95.  Both come with one years support for updates.

http://www.webroot.com/consumer/products/spysweeperwithantivirus/?id=H2-HHO_Links-SSAV&WRSID=4537a071e6e26955d8fdc8c085ab6502