恶意软件（Malware），中国大陆又称“流氓软件”，是形容网络上散播的如同「流氓」一样讨厌的软件。

符合如下条件（主要是第一条）的软件的一种称呼：

Malware, short for malicious software, is any software used to disrupt computer operations, gather sensitive information, gain access to private computer systems, or display unwanted advertising. Malicious software was called computer virus before the term malware was coined in 1990 by Yisrael Radai. The first category of malware propagation concerns parasitic software fragments that attach themselves to some existing executable content. The fragment may be machine code that infects some existing application, utility, or system program, or even the code used to boot a computer system. Malware is defined by its malicious intent, acting against the requirements of the computer user, and does not include software that causes unintentional harm due to some deficiency.