Many viruses use exotic file extensions such as .pif to hide the fact that the file attachment is executable. This email contains a harmless .pif program as a file attachment. It allows you to test how your email client reacts when you open such a file without actually causing any damage. If the red window "you are vulnerable" appears, you would have been infected.
Warning: If your provider or another mail gateway filters your emails for executable files, this email or the attachment may never reach you.