The only possible explanation is that someone unknowingly
(rogue programs are meant to deceptive) downloaded the file onto the computer and allowed the file to bypass the security alerts, if any.
Once the program is installed, there is nothing much you can do, than to pray that MBAM and other malware/spyware removal software do a good job.The best you could do, is look up anything remotely suspicious, before you accept/run/download the file.
And if you do decide to download it, scan the installation(setup) file before you proceed any further.
In your case, this example should shed some light:
^ See what the results suggest?
Edited by ReviverSoft, 08 July 2010 - 08:30 PM.