As a result of a Trojan (jamacraft\pop.exe) an overwhelming amount of malware was downloaded to several PC's. After cleaning up I found a problem with browser Internet Explorer redirecting traffic. It could not be repaired until registry entries "No update, No Repair and No modification" ahd been fixed.
Further, It seems the firmware/configuration of the router had been tampered with and was attempting to direct traffic via an unauthorised remote host. A manual reset did not help. The router had to be replaced.
For more information see another incident :-
http://tidystorm.com/423/the-redirect-virus-was-in-my-router/
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Best of Luck