Computer virus
- 2. Computer Virus: • A computer virus is a program or piece of code that is loaded onto our computer without our knowledge and runs against our wishes. • It is a harmful software program • It can replicate itself • All computer viruses are man made. Once created and released, however ,their spread is not directly under human control. • According to Webster’s collegiate Dictionary Computer virus is “a computer program usually hidden within another seemingly innocuous program that produces copies of itself and inserts them into other programs or files ,and that usually perform a malicious action “
- 3. Common virus infection symptoms • Unexplained messages appears on the screen • Specific files are mysteriously deleted • Unknown files are added to the disk • An entire disk or drive is erased • The keyboard doesn’t work properly
- 4. Worm • A worm is a special type of virus that can replicate itself and use memory, but cannot attach itself to other programs. • It uses a computer network to spread itself
- 5. Virus types: Which can be classified according to their origin techniques, types of files they infect, platform they attack etc 1.Memory resident virus vs non-memory resident virus A memory-resident virus installs itself as part of the operating system when executed, after which it remains in RAM from the time the computer is booted up to when it is shut down. Resident viruses overwrite interrupt handling code or other functions, and when the operating system attempts to access the target file or disk sector, the virus code intercepts the request and redirects the control flow to the replication module, infecting the target. In contrast, a non-memory- resident virus (or "non-resident virus"), when executed, scans the disk for targets, infects them, and then exits (i.e. it does not remain in memory after it is done executing).
- 6. Boot sector virus • Boot sector viruses specifically target the boot sector and/or the Master Boot Record (MBR) of the host's hard drive or removable storage media (flash drives, floppy disks, etc.)
- 7. Macro Virus • Many common applications, such as Microsoft Outlook and Microsoft Word, allow macro programs to be embedded in documents or emails, so that the programs may be run automatically when the document is opened. A macro virus (or "document virus") is a virus that is written in a macro language, and embedded into these documents so that when users open the file, the virus code is executed, and can infect the user's computer.
- 8. Email virus • Email virus – A virus that intentionally, rather than accidentally, uses the email system to spread. While virus infected files may be accidentally sent as email attachments, email viruses are aware of email system functions. They generally target a specific type of email system (Microsoft's Outlook is the most commonly used), harvest email addresses from various sources, and may append copies of themselves to all email sent, or may generate email messages containing copies of themselves as attachments.