The self-extracting installer in the vSphere Client Installer package in VMware vCenter 4.0 before Update 3 and 4.1 before Update 1, VMware ESXi 4.x before 4.1 Update 1, and VMware ESX 4.x before 4.1 Update 1 does not have a digital signature, which might make it easier for remote attackers to spoof the software distribution via a Trojan horse installer.