Many of the newer sites use Fast Secure Contact form. This plugin was withdrawn last weekend following the discovery that someone who had acquired it had attempted to manipulate it to show adverts for payday loans and other things. In this case it never got to the stage where it showed adverts, and everyone that has come back to me has confirmed their site has been upgraded to remove the advertising (or spamvertising as it seems to be called) code.
This is a great shame because the original plugin by Mike Challis worked really well and had a few side benefits from the earlier form manager I used about 6 years ago.
I am not going to rush into changing everyone’s forms, there is no immediate need to do this. Over the course of the next 3-6 months I will be visiting sites and checking them. If I come up with an alternative solution I will change the forms at that time and let you know so you can check they still function.