Thank you, essexboy.
I ran TDSSKiller, and it found the suspicious object in the partition. I selected delete, but Avast! put up a dialog box, and seemed to intercept the deletion. But when I ran TDSSKiller a second time, it no longer reported the suspicious object in the partition. I enclose the screenshot.
Then I downloaded ListParts and ran that, and it found a suspicious object in the partition! I’m enclosing that log as well.
Also, when I scan with Avast!, it immediately finds Alureon immediately, still in the MBR.
Thanks for your help! This is a tough case, isn’t it?