Look at the Subject of the Email

Does the subject of the email tell you it's a response to something you sent? By that I mean, does it start with RE:? If it does, does the subject look familiar? Did you really send an email to a friend that said "your web reports?" Probably not. And this is probably an indication of a virus.

Were you expecting an attachment?

Chances are you weren't. So don't open it. Even better, were you expecting a zip file? Again, don't open it. How well do you know the sender? Do they normally send you emails? Everyone notices who sends them email routinely so when an email comes in that you're not sure off with an -attachment-, please, for the sake of the internet, -don't- open it.

What is a PIF file?

It's reminiscent of an old version of Windows. There is no reason to have a PIF file anymore. DO NOT EVER open attachments that are .PIF. NEVER. EVER. If you are a Mail Systems Admin, why are you still letting PIF files through your MTA? STOP IT!