A new bug has been disclosed in Microsoft’s Windows Defender anti-virus software. Redmond bundles the service pre-loaded into every version of Windows 10. A new report shows the software is missing some files when it runs a system scan.

According to BornCity, Windows Defender ignores some files since Microsoft’s March 2020 Patch Tuesday earlier this month. Users are reporting situations where Defender is skipping over some files during a scan. It is worth noting this happens during both quick and full scans.

Defender allows users to manually exclude files from a scan. It seems Windows Defender is acting as if some files have been excluded, even if they haven’t.

Windows Defender also sends out a notification error message to the Action Center when this happens. This suggests Defender knows it is making an error or at least is operating as if files have been excluded.

“Items skipped during scan. The Windows Defender Antivirus scan skipped an item due to an exclusion or network scanning settings.”

Ongoing Patch Issues

Microsoft has yet to acknowledge the problem, but it would be another example of the company’s patches causing problems for unrelated services. Earlier this month, Patch Tuesday resulted in a new vulnerability found in the Microsoft Server Message Block (SMB) protocol being leaked.

There has been an increasing issue where Microsoft patches are fixing one issue but causing others. We have seen this recently with a fix for Windows Search that has left users unable to boot their PCs.

We may have to wait until April 2020 Patch Tuesday (April 14) to get a fix for this issue.