Summary

This virus infects lots of different executables:

When running in DOS and Windows 3.1x it will infect:

 - DOS COM files
 - DOS EXE files
 - Windows 3.x NewEXE files,
 - Windows 95 PE EXE files
 - Windows NT PE EXE files

When running in Windows 95, Windows NT and Win32s it will infect:

 - DOS COM files
 - DOS EXE files
 - Windows 95 PE EXE files
 - Windows NT PE EXE files

The virus carries a dropper of a Macintosh virus in it's code. This will work under Mac and PowerMac and will infect:

 - Mac OS applications
 - Extensions
 - Control panels
 - The System File
 - The Mac OS Finder
 - The DA Handler
 - The Desktop File

Additional Details

When Esperanto is running on a PC, it will stay resident and infect programs when they are accessed.

When such COM and EXE files are taken to a Macintosh or a PowerMac and executed under a PC emulator such as SoftPC or SoftWindows, they will execute as Mac programs. This happens because Esperanto adds a special resource-like add-on to PC files. Such programs will drop a Mac-specific virus which will continue spreading on Macintosh computers. The Mac version of the virus will not spread back to PC users. PC version of the virus won't infect Mac executables directly even if it would have access to them through floppies or file sharing.

Esperanto activates every year on July 26th. The first book in the international Esperanto language was released on this date. When an infected file is executed under Windows 95 or Windows NT on this date, the virus will show a dialog box with the following texts:

       Never mind your culture / Ne gravas via kulturo,
       Esperanto will go beyond it / Esperanto preterpasos gxin;
       never mind the differences / ne gravas la diferencoj,
       Esperanto will overcome them / Esperanto superos ilin.

       Never mind your processor / Ne gravas via procesoro,
       Esperanto will work in it / Esperanto funkcios sub gxi;
       never mind your platform / Ne gravas via platformo,
       Esperanto will infect it / Esperanto infektos gxin.

       Now not only a human language, but also a virus...
       Turning impossible into possible, Esperanto.

The Mac version of Esperanto was the first new Mac virus for over two years when it was discovered in November 1997.

[Analysis: Mikko Hypponen, F-Secure]