For default setting, the scanning area of boot up scan is different from full system scan. Then do I need to do both boot up scan and then full system scan to have 100% scan of everything?
There is no need to run a boot scan unless there is a strong indication that it is needed to solve a problem.
A full scan will do.
I believe some files cannot be scanned when Windows is running?
In theory all files will be scanned.
If after the scan avast says that certain files couldn’t be scanned, here is the explanation :
https://blog.avast.com/2014/02/28/how-do-i-handle-files-that-avast-cant-scan/
ok thanks. What kind of situation would need boot up scan? Any example?
Generally after an avast detection if it can’t be dealt with in a normal windows environment or after a detection avast suggests you run a boot-time scan.
Some may also do a boot-time scan soon after installation to give a good indication you have a clean start.
ok thx
You’re welcome.