To remove the Latest News section from the login page of the web interface, open the file:
"C:\Program Files (x86)\PRTG Network Monitor\webroot\css\styles_custom_v2.css"
and add:
.newsfeed {display:none!important; visibility: hidden; }
Save and close the file and refresh the webpage.
Tested on PRTG version 17.4.35.3441.