FRAMINGHAM (08/04/2000) - In the past two months, Microsoft Corp. has ordered 7,500 Web sites and Internet auctions to stop selling counterfeit Microsoft software. The company sent notices to another 600 Web sites this week. The software giant's secret weapon in combating piracy: an Internet monitoring tool that, according to Microsoft, sniffs out Net fraud 24 hours a day, seven days a week. The vendor is leasing the tool, an intelligent Web crawler, from the software's developer, a third-party vendor that Microsoft didn't identify. The company has been using the tool since November to detect counterfeit versions of its Windows 2000 operating system.