Methods, systems, and apparatuses, including computer programs encoded on a computer storage medium, for validating download success are disclosed. A method can include receiving a request to transmit a digital item to a computing device, transmitting a modified digital item to the computing device, and receiving confirmation that the computing device has received the modified digital item in its entirety. The method can also include for each of N invalid data portions included in the modified digital item, transmitting to the computing device a location of the invalid data portion in the modified digital item, and the existing data portion previously replaced by the invalid data portion; and receiving confirmation that the computing device has received the existing data portion. In response to receiving confirmations, an indication that the computing device has received all N existing data portions replaced by the N invalid data portions can be transmitted.