The person who used the PC must know that Windows is very sensitive to file extension, a JPG picture, renamed when the ". jpg" was deleted, the result--windows did not know it.
What about Linux? That dude doesn't look at the extension, and the software is named ". txt", so it can be executed. As for Apple Mac OS X operating system, basically between Windows and Linux-the extension is to see, but never like Microsoft's superstition file extension suffix.
Details are as follows
Mac OS X operating system when you open a file, you do not look at the file's extension first, but rather a preference to see if it has been specified open mode (the way to modify the default opening of a file, see here
);
If it is not found, find out from the resource branch which software created the file, and if neither of these information is found, determine how the file is opened by the file name extension.
So a lot of times, files without extensions can be identified and opened under Apple's Mac OS X operating system--such as Office's own installed font files--because Apple has found information in its resource branch. Who's smarter than Microsoft Windows, which only looks at the extension, no, I don't have to say.