Big read but interesting.
There are many different kinds of malware self-defense techniques and these can be classified in a variety of ways. Some of these technologies are meant to bypass antivirus signature databases, while others are meant to hinder analysis of the malicious code. One malicious program may attempt to conceal itself in the system, while another will not waste valuable processor resources on this, choosing instead to search for and counter specific types of antivirus protection. These different tactics can be classified in different ways and put into various categories.