Abstract: A Web browser or operating system of a computer maintains a historical URL list of Web sites and Web pages that have been accessed in the past. When a prescan module of antivirus software performs an initial prescan of a computer before the antivirus software is installed, it queries this historical URL list to obtain the URLs that have been accessed in the past. These URLs are sent to a URL online query service located remotely over the Internet in order to determine the status of any of these URLs. Each URL is attempted to be matched with a database of known malicious URLs including associated malicious files and associated cleanup patterns. The query service then informs the requesting computer of the status of a particular URL sent, sending back any related malicious files and any appropriate cleanup pattern. A time period associated with each URL in the database indicates when it is known that the URL was malicious.