31-03-2014, 03:07 PM
Computer Viruses and Worms
Computer Viruses.ppt (Size: 338 KB / Downloads: 107)
Viruses
A virus is a small piece of
software that piggybacks on
real programs.
2 main characteristics of viruses
It must execute itself.
It must replicate itself.
Virus might attach itself to a program such
as spreadsheet. Each time the spreadsheet
program runs, the virus runs too and
replicate itself.
E-mail Viruses
Moves around in e-mail messages
Usually replicate itself by automatically mailing itself to dozens of people in the victim’s email address book.
Example “MELISSA VIRUS”
Example “I LOVE YOU VIRUS”
WORMS
Small piece of software that uses computer networks and security holes to replicate itself.
Copy of the worm scans the network for another machine that has a specific security hole.
Copy itself to the new machine using the security hole and start replicating.
Example “CODE RED”
Difference between Virus and Worm
The difference between a worm and a virus is that a virus does not have a propagation vector. i.e., it will only effect one host and does not propagate to other hosts. Worms propagate and infect other computers. Majority of threats are actually worms that propagate to other hosts.
Melissa Virus (March 1999)
Melissa virus spread in Microsoft Word documents sent via e-mail.
How it works ?
Created the virus as word document
Uploaded to an internet newsgroup
Anyone who download the document and opened it would trigger the virus.
Send friendly email messages to first 50 people in person’s address book.
Symptoms of Infection
Programs take longer to load than normal.
Computer’s hard drive constantly runs out of free space.
The floppy disk drive or hard drive runs when you are not using it.
New files keep appearing on the system and you don’t know where it come frm.