mstbl.ocx definition, relationships, removal:

This is a part of a malicious parasite that violates user privacy and damages the compromised system. The mstbl.ocx file can be used for different purposes depending on the related parasite's type, functionality and carried payload. Although mstbl.ocx may not take any malicious actions by itself, it ensures that a parasite is working properly and therefore needs to be removed. DO NOT open, execute or edit mstbl.ocx!
The mstbl.ocx file is installed and used by IELoader.
Please note that the mstbl.ocx file actually may be a fully legitimate part of the operating system or legitimate software. Often parasites use files with unsuspicious names, but malicious functionality. You should always carefully check the file before deleting it. It may not be related with malware, but can be required by your essential programs to work properly.