I'm not familiar with that plugin but if you want to try-
Go to Admin CP -> Plugins & Products -> Plugin Manager
Edit the Plugin titled:
Check if NoSpam! (img) question has been answered correctly (Register)
In the PHP code- put this code at the VERY TOP
Code:
if (THIS_SCRIPT == 'register')
{
and put this code at the very bottom:
That will basically tell the plugin to only run on the built in register.php page.
Hopefully steam connect uses its own php page so this may work.