Are you using the Google PageSpeed module on your site?  If you haven’t updated it recently, you will probably receive an alert from Google reminding you to update it.

Here is a copy of the letter that Glen Gabe shared.

It seems that many were sent because there are a lot of reports from others who also received the same update recommendation.

John Mueller from Google also commented on the letters.  And it sounds as though this isn’t a result of a specific hack or exploit but rather just a regular alert.

This isn’t the first time Google has sent out these types of warnings.  Google often sends out emails reminding site owners to update WordPress and other CMS when Google can identify when an older version is being used.

So if you recieve one of these letters, it won’t affect your site’s quality or ranking.  But as with any CMS plugin or module, you want to update them regularly to decrease the chance your site will be exploited by an unpatched issue.