‘Login’ is a noun (or sometimes and adjective). ‘Log in’ is the verb. Thus, ‘Click here to login’ is incorrect. (Backup is a similar story.)
I have, in the past, pointed this out to folks, but I think I’m going to give up. More and more major corporations with the resources to hire people who know what they’re doing are using ‘to login’. The one that hurts the most is not a major corporation, however, it’s Writing.com.
I tell myself that this is just the natural process of the evolution of the language, but in this particular case it bugs me beyond any rational explanation. I guess we all have our language peeves, and it’s time to let go of mine. Instead I’ll climb on my motor-cycle, go down to the base ball game and heckle the numpire.