After analyzing data from more than 600 million systems around the globe, Microsoft has determined that zero-day vulnerabilities aren't nearly as worrisome as malware based on traditional techniques, such as social engineering and unpatched security holes. It's not that zero-day threats aren't inherently dangerous, it's just that hardly anyone's exploiting them, at least comparatively
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Maximum PC | Microsoft Intelligence Report Downplays Prominence of Zero-Day Threats