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The Nimda worm modifies all web content files it finds. As a result, any user browsing web content on the system, whether via the file system or via a web server, may download a copy of the worm. Some browsers may automatically execute the downloaded copy, thereby, infecting the browsing system. The high scanning rate of the Nimda worm may also cause bandwidth denial-of-service conditions on networks with infected machines and allow intruders the ability to execute arbitrary commands within the Local System security context on machines running the unpatched versions of IIS.