OK, this will probably take more analysis as you are on a 64bit OS version so care has to be taken not to try fixing the MBR or you could have an expensive paper weight.

Other than the unknown MBR code, which is likely to be because you have an HP system, is that correct ?

If so it has a recovery partition and a recovery console, in order to access them HP is likely to have a custom MBR code, hence the unknown MBR code line. So you don’t want to touch that or you would no longer have access to this recovery partition or recovery console.

So other than your case of paranoia mentioned in your first post are you experiencing any symptoms (strange occurrences, etc.) ?

If you can open the avast chest (avastUI, Maintenance, Virus Chest) and right click on the file that was detected as MBR:Alureon [Rtk] and select Properties. What was the original file name and the location where it was found ?