The installer sets this variable to the abbreviated MDAC (Microsoft Data Access Components) version number if MDAC is present on the target system, or to 0 if not present. The MDAC version is encoded as 100 * major + minor; lesser version number parts are ignored. For example, MDAC version 2.81.1117.0 would be encoded as 281. For a more detailed MDAC version number, you can use the RegMDACVersion instead.
You can refer to this variable as <VersionMDAC>. In conditional expressions you can omit the brackets and simply use expressions like VersionMDAC >= 280 as a test for minimum MDAC versions. Do not change its value; it has been carefully configured for cross-platform compatibility and is used internally by the installer.