http://www.twcenter.net/forums/showthread.php?731465-WARHAMMER-Radious-Total-Units-Mod-%28Released-30-5-2016%29&p=14991417 is not an official Steam site.

Never enter your Steam password on an untrusted website. Any login form on an official Steam site will display “Valve Corp.” in green with a padlock icon in your browser’s address bar, as shown below:

Valve Corp. [US]