Malware is a piece of code that is malicious in nature. Malicious code can be a software, an intrusive software . It can steal, encrypt, or delete your data, alter or hijack core computer functions, and spy on your computer activity without your knowledge or permission. It consumers computer memory to replicate and attach themselves to other programs to create congestion and affect the performance of computer , resulting the server failure or drastic increase in spam traffic. Some examples of malware are virus , spyware, trojan horse , adware, worms etc.