An Issue with avast! 4x & 5x following symbolic links back to the host OS when scanning an offline OS.
In other words....
I pull a hard drive from a Windows Vista computer, and put in in an external enclosure to preform an offline scan with my host computer (Windows 7)
avast! 4x or 5x is set to scan just the offline OS hard drive (drive Y:), using a custom scan.
When avast hits the symbolic link for Documents and Settings located on the offline OS drive, at "Y:\Documents and Settings" , it follows the link back to my host computers Users folder, at "c:\Users" - even though I selected only drive Y: to be scanned through "Interactive Selection".
The result.... and additional 60min to my scan while it checks my host computers 100+ GB "users" folder
This issue has been around since at least version 4x, and effects both Vista and Windows 7 (as either the host or the offline system).
The fix... in your custom scan settings, add an Exclusion to the symbolic link "Y:\Documents and Settings\"
I was surprised to not see this fixed in avast! 5x, and also surprised to not see any mention of it in the forums here. I suppose if I had taken the time to contact customer support, it may have been fixed. But I thought I might at lease save some other users some time by posting the issue and the fix here..... I waited through several excessively long scans before I even realized what was going on.