Speaking at a London press conference earlier this month, Jim Ewel, Microsoft vice president for IT infrastructure and hosting, announced that the upcoming Windows release known as "Whistler" will include a range of new security options, including one that will block any software lacking a valid digital signature.

Though implemented in response to e-mail-attachment viruses like the "Love" bug and Melissa, the new feature will extend to "every piece of code executing on the machine," Ewel told British reporters.

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