As pointed out above, here is an update on this. Per the link: A recent update to Windows Defender has caused it to incorrectly identify SupportAssist as malware. Dell is working closely with Microsoft to resolve this issue and correct the false positive. * User with SupportAssist auto updates enabled should not be impacted* User with SupportAssist auto updates disabled should update Microsoft Defender virus definitions to version 1.359.1239.0 or higher  
Is this a known false positive? This reddit page seems to indicate the problem is widespread. i cant remove or put in quarantine "trojan:html/cryptostealbtc" : antivirus (reddit.com)  
Dell Update triggers CryptoStealBTC warning with Microsoft Antimalware