Nowadays, malicious codes are significantly increasing, leading to serious damages to information
systems. It is worth to note that these codes generally depend on the rootkit techniques to make it
more difficult for themselves to be analyzed and detected. Therefore, it is of paramount importance
to research the rootkits to effectively defend against malicious codes. In this paper, we explore and
survey the rootkit techniques both in user-level and kernel-level. Several rootkit samples are also
utilized for the test and verification purpose.