Virus.DOS.Agena.723, also known as Agena, is a resident infector MS-DOS virus.
Agena is a memory resident, file infecting computer virus which infects .COM and .EXE files, including command.com. Agena becomes memory resident at the top of system memory but below the 640K DOS boundary. Once it is memory resident, Agena infects .COM and .EXE files as they are executed. Infected programs will have a file length increase of 723 to 738 bytes with the virus being located at the end of the file. An infected file's date and time in the DOS disk directory listing are not altered. Total system and available free memory, as indicated by the DOS CHKDSK program, will have decreased by 1,296 bytes. Interrupts 20 and 21 are hooked by the virus. It is unknown what Agena may do besides replicate. No text strings are visible within the viral code in infected programs.
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