That message is generated by Javascript within a web page. However I've never seen that message here on Answerbank. Further, I've just examined the source code for a few pages here and, while Javascript is used for other purposes, the code to generate that message simply isn't present.
That leads me to suspect that you've got MALWARE on your computer, that's injecting the relevant code into the pages that you're viewing for some strange reason.
Download, install and run the free version of Malwarebytes Anti-Malware to see if that fixes your problem:
https://www.malwarebytes.org/antimalware/
(NB: At the end of the installation process you'll encounter a pre-ticked box which invites you take a free trial of the Premium version of the program. Ensure that you remove the tick before proceeding further).
Also clear your browser's cache:
http://uk.pcmag.com/browsers-reviews-and/41051/feature/how-to-clear-your-cache-on-any-browser