Electical Outets with Bootleg ground
Bootleg ground is always super bad

Bootlegging ground (faking a ground by attaching it to neutral) is always bad. 

The reason is that neutral is not safe! 

In a perfect world, neutral is near zero volts.  But lots of perfectly ordinary failures can happen where neutral is hot and dangerous. These ordinary failures should not make your system dangerous.  And that's why we insulate neutral.  

A simple neutral break will cause the neutral wire (downline of the break) to become energized. If you  have tied ground to it, now the chassis of the machine is also energized.

So no bootlegging ground!  Try to avoid it even on dryers and ranges where it is legal due to a special exception.  When  you have a 3-prong dryer or range, that is ungrounded (the funny wire is neutral not ground). Use the "GFCI Breaker" or "Retrofit ground" option below. 

What can you do instead?

First, you can roll them back to a 2-prong receptacle. I gather that option is not acceptable to you. However, you must, unless you go with another option. 

Second option and an easy bolt-up: install GFCI protection, one way or the other: 


Fit a GFCI receptacle at this location. Label it "No Equipment Ground". 
Place a GFCI device somewhere else, so that this receptacle is fed off that GFCI's "Load" terminals.  Fit a plain 3-prong receptacle, and label it "GFCI Protected / No Equipment Ground".


You're welcome to use a GFCI breaker as the GFCI device. (this is the only viable way to do a 240V load).  



Third, an option is to retrofit a ground wire. They greatly liberalized the rules for doing this in 2014.  Run any large enough bare or green copper wire from this location to any other junction box that has a large enough ground wire (or metal conduit) back to the panel, or to the house's Grounding Electrode System wires (i.e. the thick bare copper wires between water pipe and panel), or to the panel itself obviously.  You cannot attach to a water pipe.