If you are an owner of a Smith & Wesson M&P Shield, you need to immediately cease using the gun and check it against the following inspection.
And here’s a video S&W produced that explains how to check for the problem:
This applies to pretty much any and every Shield produced since they first hit the market. S&W believes it affects only a small number of pistols, but better safe than sorry. And truly in this case, it is about being safe as this issue pertains to the mechanical safety mechanisms of the firearm.
I just checked my own Shield and it did not exhibit the problem.
Check yours now.