We have a lot of news connected with penalties from Google this month and with this article we will continue the trend. If you are checking Google announcements regularly this will not be any new information for you. Google already warned webmasters about penalties if they are using sneaky mobile redirects in October last year.
With no specific reason for the announcement, they decided to warn us again. This happened on the 4th of May, in Google+. Here is the exact part about these mobile redirects:
To combat this trend, we have been taking action on sites that sneakily redirect users in this way. If your site has been affected, read this Help Center article on detecting and getting rid of unwanted sneaky mobile redirects.
As we saw during the previous month Google are trying to prevent of spam activities and are taking all the possible actions. For this reason I thought that Google already took some actions to prevent or even penalize webmasters who are using this technique. It seems I was wrong, so my second guess is that this is a last time warning and probably many webmasters are using this sneaky method. Maybe the volume of using this technique increased a lot during the last months and actions just needed to be taken.