I'm not sure why MBAM can't update on a limited account, it stores its database in the all users application data, which can be written to from the Guest account (I just tried creating a text file, and it worked). I think it's best to run MBAM under an admin account, since it needs to load its driver for direct disk access. Programs that are run under limited accounts do not have permission to load drivers (I think, not 100% sure). Also, if you run it under an admin account, you shouldn't have to run it on any other user's accounts, since MBAM is capable of finding the paths to other user's files (open MBAM, go to 'More Tools' tab, and click 'Collect Information'. It will find everyone's folder locations).