From threatpost.com:
Researchers have developed a method for bypassing Windows Defender that will allow any malware to execute on a Windows machine. Microsoft, meanwhile, has told the experts that it does not see this as a security issue and will not address the problem in its native antimalware protection.
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The bypass involves the use of a custom-built SMB server, tricking Windows Defender into scanning a benign file, and executing a malicious one instead that is passed to the operating system.
Full article here.