1. A control method by an information processing system including a plurality of computers, the plurality of computers including a first computer, a second computer, and a third computer, the control method comprising: storing, by the first computer, identification information of a user and identification information of a computer among the plurality of computers in association with each other in a memory, the computer executing a software of the user, the software being related to a virtual machine; extracting, by the first computer, identification information of the third computer already executing the software of a target user from the memory based on identification information of the target user, when it is detected that the software of the target user is activated in the second computer and when identification information of the target user is stored in the memory; transmitting, by the first computer, the extracted identification information of the third computer to the second computer; receiving, by the second computer, the identification information of the third computer from the first computer; allowing, by the second computer, the second computer to transmit broadcast data corresponding to the software of the target user to the third computer, when the broadcast data is received; determining, by the second computer, whether another software which is different from the target user, is already executed in the second computer when the software of the target user is activated in the second computer; and transmitting, by the second computer, an activation notification including the identification information of the target user and identification information of the second computer to the first computer, when it is determined that the another software is not already executed.