Nr Virus

Virus Name: Nr Aliases: Nr.300 V Status: New Discovered: July, 1995 Symptoms: .COM file growth; file date/time changes; decrease in available free memory Origin: Unknown Eff Length: 300 Bytes Type Code: PRhCK - Parasitic Resident .COM Infector Detection Method: NAV, NAVDX, ViruScan, IBMAV, VAlert, AVTK, F-Prot, ChAV, NAV/N, IBMAV/N, NShld, NProt, AVTK/N, Innoc Removal Instructions: Delete infected files General Comments: The Nr or Nr.300 virus was received in July, 1995. Its origin or point of isolation is unknown. Nr is a memory resident infector of .COM files, including COMMAND.COM. It is not related to the NR-481 virus. When the first Nr infected program is executed, this virus will install itself memory resident at the top of system memory but below the 640K DOS boundary, not moving interrupt 12's return. Available free memory, as indicated by the DOS CHKDSK program from DOS 5.0, will have decreased by 320 bytes. Interrupt 21 will be hooked by the virus in memory. Once the Nr virus is memory resident, it will infect .COM files, including COMMAND.COM, when they are executed. Infected .COM files will have a file length increase of 300 bytes with the virus being located at the end of the file. The program's date and time in the DOS disk directory listing will have been updated to the current system date and time when infection occurred. The following text string is visible within the viral code: "Nrt7" Additionally, the text string "Nr" can be found starting in the fourth byte of all infected files.