Ada (computer virus)
Ada is a computer virus that can affect any of the DOS operating systems. Ada was first discovered in 1991.

History
Ada virus was first discovered in Argentina in .

Characteristics
Ada is a memory resident virus that infects files. The Ada virus mainly targets .COM files, specifically COMMAND.COM and stays in the memory of the computer it infects after the program it infected executes.

Infected programs have 2,600 bytes additional data inserted at the beginning of the file, and the file itself contains the text strings:
 COMMAND.COM
 PCCILLIN.COM
 PCCILLIN.IMG
 HATI-HATI !! ADA VIRUS DISINI !!Delete

Another version of Ada has these text strings along with the strings BASURA BASURA repeated numerous times.

Computers infected with the Ada virus often have a slow clicking sound emitting from their speakers; this clicking may sometimes change in pitch. Infected computers may show a "Disk Full" error even if the disk still has space on it.

While infected with the Ada virus, system memory measured by the DOS CHKDSK decreases by 21,296 bytes to 21,312 bytes. The virus resides in the memory after an infected file is run and will infect any other .COM files executed on the computer. It also hijacks interrupts 08, 13 and 21.

Infection route
There is only one way to infect a computer with the Ada virus; by executing an infected file. The infected file may come from a variety of sources: floppy disks, files downloaded from the Internet, and infected networks.

References

DOS file viruses