The Blackdeath virus activates every Friday the 13th, displaying a few messages and deleting some critical system files, such as Windows, Program Files, and many more.
According to the pop-up windows of the virus, BlackDeath was written on 06/06/1997 - a week before a Friday the 13th.
When BlackDeath is opened on any day that is not Friday the 13th, a word document is opened that says nothing but WM.Blackdeath. The macros in the file are not activated. However, when the user opens BlackDeath on Friday the 13th, a window pops up that reads 'Your computer is now lost to the ages...' and when the OK button is clicked, 'WM.Blackdeath' is displayed with another OK button. Once clicked again, it displays 'Written on 6/6/1997' with yet another button.
Once the windows are cleared, if the computer is restarted, a black screen is displayed when the computer regains power. The screen will read:
The following file is missing or corrupted: COMMAND.COM
Type the name of the Command Interpreter (e.g., C:\WINDOWS\COMMAND.COM)The computer, at this point, is entirely unusable.
Watch the virus work here.