**2.2 Malware mechanism as backdoor and logic bombs**

The Previously discussed malwares are all have common thing as they are independent program developed and they are developed for malicious actions. Some malwares are not fit into this category as they are independent programs but code chunks that can be inserted into other applications for bad intentions [8–10]. Most common malware in this category are backdoors and logic bombs [8] Backdoors appear when programmer give themselves or others means for future access to a system. The tricks can be used here by simply making programming easier in ways to avoid logging in with user credentials or some mechanisms to allow access later when it happens that users accidently lock themselves out from their systems. End-users usually they not want the vendor to gain access to the system by installing these scripts or piece of code especially that backdoors might be fallen into the wrong persons' hands. Backdoors can be happened with different ways as hardcoded account as certain user name and password are always used to provide access to the system. In some scenarios, when the end-users always use the default password as users forget or not bother to change and finally, there is always possibility to unknown access channels that can access the system by avoiding usual authentication processes. Logic bombs is another kind of malware that works by modifying existing code. In this type, some certain conditions (as specific date or time occurring, specific information in the file's content or specific results from API calls) can be coded to trigger payload of harmful action to be executed [9, 10]. Logic bombs scenarios examples can be explained as certain programmer employee created malicious payload that it is inactivated as long as he/ she appears in the system daily, once he/she disappeared as being fired for example, the harmful payload then can be activated.
