Provided are a mobile device having a self-defense function against virus and network-based attacks and a self-defense method using the same. The mobile device includes a virus checking module, which receives information on files required for virus checking on a basis of input/output (I/O) information created from a file system of an operating system, and determines whether or not the files are infected with a virus using distribution of similarity between data; a malicious packet determination module, which examines information on an Internet protocol (IP) packet created from a network to interrupt a denial-of-service attack (DoS attack); and a control module, which receives the I/O information created from the file system of the operating system, selects the files required for the virus checking, and transmits the selected files to the virus checking module, or receives information on the IP packet created from the network to transmit the received information to the malicious packet determination module, thereby preventing damage caused by the virus in advance, and effectively preventing a denial-of-service attack (DoS attack) caused by wireless network resource depletion and battery consumption that may occur in a wireless environment.