MALICIOUS SOFTWARE What is malicious software? A software that has been intentionally included or inserted in a system , mainly for any harmful purpose. They are mainly of 2 categories:  1. A Host Program(fragments of program ,cannot exist independently.)                                                             eg:virus,logic bombs ,backdoors                                                        2. Independent(self contained programs)                                                               eg:worms,zombies  VIRUS Attaches itself to another program and propagates copies of itself to other programs.It is a piece of software that infect other programs by modifying them like copying o the virus program and therby attack other programs. BACKDOOR It is also known as trapdoor,is a secret entity into a program that allows someone that allows someone that is aware of the backdoor to gain access without going through usual security procedures.  Programmers have been using this for debugging and testing programmes.The backdoor is code that recognize some special sequence of input or is triggered by being run from a certain user ID or by an unlikely sequence of events.. LOGIC BOMB One of the oldestthreat,a code embedded in some legitimate program that is set to explode when some conditions are met.Conditions can be the prescence or abscence of certain files.,a particular day of the week,etc. Nature of virus There are four phases in the lifetime of virus. Dormant phase:   The virus is idle. Propagation Phase: The virus places an identical copy of itself into other programs Triggering phase: The virus is activated to do the function. Execution phase: The function is performed. Types of virus 1.Parasitic virus 2.Memory resident virus 3.Boot sector virus 4.Stealth virus 5.Polymorphic virus 6.Metamorphic virus Macro viruses: macro viruse are platform independent.They mostly infect Microsoft word documents.They are easily spread .A very common method is electronic mail. Viruses used to take months or years to propagate but now they take just seconds.This makes it difficult for antivirus software to respond befor much damage is done.A greater degree of security is needed to  be built to counter the growing threat.