Type Boot sector virus
Date Discovered 1988.01
Place of Origin United States
Source Language
Platform DOS
Infection Length 1 boot sector
Reported Costs

Pentagon is a boot sector virus from 1988. The virus deletes the Brain virus and predates Denzuko, a more famous and popular virus that does the same thing.


When a disk infected with Pentagon is booted, the virus will become memory resident, occupying 5 kilobytes of RAM. The virus also contains two files, one named 0F9H (the number 249 in hexadecimal) and another named PENTAGON.TXT. 0F9H contains viral code that would not fit in a single boot sector as well as the original boot sector of the infected disk. PENTAGON.TXT is simply an empty file.

It infects 360 kilobyte floppies. Infected floppies can be identified by the string "HAL". It searches for and removes any copy of the Brain virus it finds. Parts of Pentagon are encrypted.

Other Facts

The string "HAL" found in the virus is the name of a fictional computer in 2001: A Space Odyssey as well as the letters "IBM" each shifted back through the alphabet. The virus was thought to be extinct in the wild. Though nematodes have existed since the first malware, Reaper, Pentagon is the first nematode virus.


Patricia Hoffman. Online VSUM, Pentagon Virus.

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