> Even more worrying is the shops that claimed the systems had viruses and they installed antivirus software - conveniently the paper authors weren't able to find any activity log data on those machines. That suggests that some repair techs are actively cleaning up their tracks.

This is the conclusion that the researchers imply, but keep in mind that these computers did have malware on them: the spyware the researchers planted there! As a former repair tech, if I’d seen some thing writing screenshots and activity logs to disk (we would use, among other things, sysinternals tools like procmon to look for malware) I would definitely be deleting that.

Regardless, the fact of the matter is that a negative finding in this study is meaningless, since the laptops could have had the disks removed and imaged separately, or the techs could have booted a live USB to copy off files. The researchers’ spyware would have not noticed in these cases. It is concerning to me (in terms of the quality of the overall research) that this is not mentioned in the limitations section of the paper given how obvious it is.