The reputation of an executable computer program is checked when a user input to a computing device initiates a program launch, thus triggering a check of a local cache of reputation information. If the local cache confirms that the program is safe, it is permitted to launch, typically without notifying the user that a reputation check has been made. If the local cache cannot confirm the safety of the program, a reputation check is made by accessing a reputation service in the cloud. If the reputation service identifies the program as safe, it returns an indication to the computing device and the program is permitted to be launched, again without notifying the user that a reputation check has been made. If the reputation service identifies the program as unsafe or potentially unsafe, or does not recognize it at all, a warning is displayed to the user.