Using Avast I got some items in 'System Volume Information' and could not be deleted. It seems others have had this kind of issue
You already answered the question of how it got there. The Trojan did not put it into the System Volume Information Folder; The System Restore Service did.
System Restore checkpointed and a Trojan was in one of the monitored locations, so it got saved as part of the checkpoint.
Avast can view the contents of the folder, just as you can; run a command prompt as administrator and you can easily view the contents of the folder. You can even change or delete the contents of the folder. I don't know why Avast would have issues deleting the files.
Cannot Remove Trojan Win32
The Error message makes it pretty clear. It has NOTHING to do with the file being in System Volume Information at all:
The Operation is not supported for this type of Archive
Cannt process "C:\System Volume Information\restore{07AAAC-1E84-4982-B148-C6D063D1AA98\A0003837.msi\icon.icon.exe "[b][/b]
The Error is because Avast does not support deleting files from .MSI installers. IT has nothing to do with System Volume Information.
the .msi is probably an installer for a piece of software that installs adware in addition to it's typical complement. Why they decided to mention anything about a Trojan I haven't a clue, considering they quite mention it is a Win32:Adware-gen that is causing the issue.
The Avast forum did not, IMO, give a quick and easy answer to the problem.
Uh, actually, it gives several.
It would seem the Trojan creators have got Windows by the tail. Just put it into the 'System Volume Information' and nobody can get rid of it.
It failed to delete the file because it's inside an MSI file and Avast's MSI support does not include removing files, only reading them.