Telcom company injecting javascript in the header of a web-page

Question

The start page of my browser is example.com.

Recently, connecting through the main Spanish telcom network (Movistar), I got a different page, with a header showing the name of the this company.

This is the js:

setInterval(function(){if(!document.getElementById('OPTSmartBannerScript')){var js = document.createElement('script');js.id = 'OPTSmartBannerScript';js.src = 'https://conexionseguraempresas.movistar.es/public/SecureBar/icon.js?preview=0&type=degustacion';var first = document.getElementsByTagName('script')[0];first.parentNode.insertBefore(js, first);}},1000);var g_icon_parameters = { "servicesStatus" : "W=1;V=1;P=1;"}

What's the point of this?

I do not suspect a real scam behind this, but if they mess with this page, how to know they don't mess with other pages?

Answer 1

How to know they don't mess with other pages?

Use HTTPS to ensure nobody messes in-transit with the pages you receive.

‎

What's the point of this?

This seem to be part of a service called conexion segura (safe connection) that checks the reputation of the pages you load:

The Conexión Segura service checks the reputation of the web page and, should it be of doubtful reputation, it alerts you blocking the access, that may be continued under your own responsability.

This way, it will keep you safe in real time from potential threats of Malware and Fraud (Phishing identity impersonations) types.

Its activation is immediate and independent of the OS, as well as of the device you use to browse.

Translated from http://www.movistar.es/particulares/conexion-segura/

It seems you have accessed a page that was flagged by them as suspicious, and this system replaced it on the fly with a warning page that would allow you to proceed if so you wish.

According to the providing information, this service can be enabled and disabled at their portal page by the owner of the connection.