The word Advertising sometimes appears on the site, what is it?

Question

Malware

There is a site, a couple of months ago I began to notice that from mobile browsers sometimes the word Advertising cuts into the text on any page. There is no advertising itself, just this word. When updating, it disappears, then it does not appear soon. There is no such thing from the desktop. There is nothing in the code from the desktop and from the android either. How to catch is not clear. Google is silent on this matter.
If a virus, then strange, why is it so rare, and there is no advertising itself.
For example:

Answer 1

Exactly the same problem, no solution so far? I also broke my head with this, then it appears then no.

Answer 2

Perhaps installing an SSL certificate will save you. Somewhere here on the forum I asked a similar question. The customer had a MegaFon operator on a mobile device, from which he went to his admin panel, which I wrote for him, saw an ad. Installed an SSL certificate and everything is back to normal.