VirusesBy siddesh sangodkar

Virus•> parts•> phase•> code

Computer virus

•Virus is a fragment of code that is •embedded within a legitimate code which

is able to self-replicate and designed to infect other programs.

•They can modify and destroy files and cause system crashes and program malfunction.

Parts of a virus

•A computer virus has three main parts:• a mission component: •a trigger mechanism•a self-propagation component.

a mission component

•The mission component is the executor of the deed the viruses designed to accomplisherasure:of all data on a computer system. The mission component lies dormant until activated by the trigger mechanism.

a trigger mechanism

•The trigger mechanism tests one or more aspects of the system state such as the current date to determine whether to activate the Mission component. For example, a possible virus may be of the form: if today‘s date is 24/9/13 then erase all accessible data on the computer system , otherwise propagate self.

the self-propagation component

•The third part of the virus,the self-propagation component, allows the virus to quickly spread to other programs to which the virusis not already

attached

Phases of a computer virus•First phase : Placement of the code Placement of the where it may be executed.

Eg modification of .exe files ,boot sector,device drivers.

• Second phase: Saving the codeit involves saving the code in the storage devices,to make it difficult to remove and delete.Eg viruses may be hidden in the hard disk in boot sector ,.exe files etc

Phases of a computer virus

•Third phase: test for a condition

Involves testing for a condition ,which if met will activate the virus.a condition may be a specified time,date or after a specified no of copies of the viral code hav been made.

•Fourth phase: action phase

during this phase,the virus attacks the target system.and the effects of the attack may be destructive or non- destructive.

code

references

•Operating systems by william stallings pg 651

Semester questions:>What ia virus? Explain different phases of virus.also with the symbolic code explain the virus structure. - 7 mks>write a short note on viruses. - 4 mks>what are the different phases of virus?explain - 6 mks>explain the nature of virus and explain different types of viruses. -10 mks

Thank you………