Winstart.bat was also used to load memory-resident utilities in Windows applications in order to run DOS applications under Microsoft Windows version 3.00 as described in Microsoft Article ID: 69186 but in could be misused for malicious purposes. Winstart.bat was used on older Windows Operating Systems like Windows 95, 98 and ME and was executed every time Windows starts just like AUTOEXEC.BAT as described here. Winstart.bat is a batch File (text file) which contains commands that can be used to run other processes or tasks when you execute it and is usually located in the C:\Windows folder. When doing a Google Search for Avast C:\Windows\winstart.bat file is offline, it appears that avast is the only security vendor providing that message and has been doing so for several years. The error message you received is common among avast! users.
