Malware comes with DLL Hijacking Feature. Trojan Dropper.UAJ hijacks a library file called comres.dll, altering it to ensure that each time it’s being used, the malware steps into play. The Trojan then drops a Backdoor, identified by Bitdefender as Backdoor.Zxshell.B, which actually contains the code compromising the system. The Trojan is able to run on Windows7, Windows Vista, Windows 2003, Windows 2000 or Windows NT in both 32- and 64-bit environments.
Source: https://thehackernews.com/2012/02/dropper-malware-comes-with-dll.html