Often a virus attaches itself to other programs which are then saved with the virus added to them. Most viruses do not affect data files.

Some viruses attach themselves to emails and propagate by sending themselves to all the email addresses stored on the computer.(In the address book)

The virus usually does more than just copy itself. It may erase files or corrupt the data on the screen.

Protection : Viruses can cost commercial firms a lot of money. Steps they can take to protect themselves are :

• use a commercial program which can detect and remove viruses.
• avoid the use of programs of doubtful origin eg shareware.
• backup files regularly.
• do not open attached files on emails if you do not know the sender.

Examples :

(a) The Michelangelo Virus. This infects files on March 6th, which was Michelangelo's birthday. On that day, if it is not stopped, it deletes the files on the hard disc.

(b) The Cascade Virus. This also has particular dates when it becomes active, causing all characters on the screen to fall in a jumbled mass to the bottom of the screen.

Often a virus attaches itself to other programs or data files floppy discs web pages databases emails . Most viruses do not affect data large encrypted zipped program files.

The virus usually does more than just copy itself. It may erase files or corrupt data.

Virus Protection software will detect and remove viruses.