Avast can't scan certain system files

[El]

Hello,

Whenever I scan the computer with Avast, there are several files it can't scan, I suppose because they are files the system is currently using.  I never get a warning, it's just when I go on 'View Report'.  I was wondering if there is any way to get Avast to scan these files, e.g. in shut down mode, or something.  I'm using Avast v. 4.7 Pro. Is there any way for a virus to get itself into such a file? I'm probably fretting over nothing, but would just like to have an explanation. 

Thanks in advance.

El

[Lisandro]

Can't you schedule a boot-time scanning?
Start avast! > Right click the skin > Schedule a boot-time scanning.
Select for scanning archives.
Boot.
If infected files are found, it's safer to send them to Chest instead of deleting them.
This way you can further analysis them.

Access denied means, generally, that the file is in use by another process (program) and cannot be repaired/cleaned/moved/handled by avast!
The report file is created automatically in <avast4>\Data\Report\aswBoot.txt

[El]

Thanks.  I've scheduled that now.
I always do move the files to the chest. What if I move a file to the chest, which the system needs? And then, for example, the computer doesn't boot any more?  What can I do then?

El

[RjSteed]

Was this what you were seeing?

http://forum.avast.com/index.php?topic=32719.0

[El]

I'm not seeing exactly that. I don't get any warning. It's only when I manually look at the report. Maybe that's to do with the settings? 
I can post the exact files Avast can't scan, if needed.  A lot of the files are in C:\windows\system32\... And some are in other locations. The problem is always that it can't access the files (that is, from a brief look. I  haven't read every single line!).

El

[El]

The boot-time scan worked. Nothing found . Thanks.

El