The Problem:-whenever I try to install DirectX 9.0c, it pops up the following message:-"a cabinet file nessesary for installion cannot be trusted."
Cause:-This problem happens in most cases due to system corruption or if users disabling their cryptography services.
Resolution:-Make sure your Cryptography services are enabled.To do this:-
1]Click Start>Run>Type services.msc>OK
2]Now in the Services(Local) list scroll down to Cryptographic Services.
3]Right click on it and select Properties;make sure that the Stratup type of this service is Automatic.If not make it Automatic
4]Also make sure that this service has strated;if not then click the Start button.
Make sure to remove temporary files in %temp% and (if installing end-user runtime)%windir%\system32\directx\websetup Error.
Other things to do:-
Chkdsk the drive.
Scan your system with latest versions of Spybot,Search and Destroy,CWShredder as well as with Adaware.Run all of them in safe mode.
Free online scan is available here:-http://housecall.trendmicro.com/
Also make sure that you are downloading DirectX 9.0c from a trust worthy site,i.e.-http://www.microsoft.com/windows/directx/default.aspx