With the rapid development of Internet technology,the network has become increasingly important in people's production and life.However,the destruction of computer viruses and the intrusion of various Trojan horses may lead to the theft of personal data and even the collapse of computer systems.This paper will define computer virus,list the main types of existing viruses,analyze the characteristics of computer virus in the online environment,and provide some security protective measures,aiming to provide users with reference and suggestions.