Yeah the makecab.exe program is used to compressed CBS log files which can be large files. When windows scans for updates upon boot-up it often finds these CBS logs and compresses them, and the compression is done withe the makecab.exe program. I do not know if there are any CBS file scans being done while downloading, but it definitely is possible. If there are not a lot of resources being used up you shouldn't worry, that is just an autorun program doing its job. This is not abnormal, I have heard of makecab running while downloading before so I don't think there is a lot to worry about.