Bug in Microsoft Security Essentials Downs Windows XP Machines

An update to Microsoft Security Essentials, the software company's free anti-malware software, crashed Windows XP computers last week, causing business disruptions to customers still relying on the outdated—and, in many cases, now-unsupported—operating system.

While uninstalling Microsoft Security Essentials worked around the issue, it also caused an additional problem: Even though Microsoft later fixed the update, MSE could not be reinstalled on Windows XP computers because the systems are no longer supported by Microsoft, the source said.