Form now on I highly recommend this Avast Pro - exclusively to my enemies!
False positives happens, and it is not only avast

http://www.theregister.co.uk/2013/11/07/kaspersky_update_borks_nhsnet/

https://www.itnews.com.au/news/webroot-bricks-windows-pcs-after-flagging-system-files-as-malware-459511

https://forums.theregister.co.uk/forum/1/2010/03/22/bitdefender_dodgy_update/

It has happend do evry AV vendor and will happen again