I watch what I read carefully and this one seems to be popping up more and more often. At work I see this written in memos, emails and even in the comments section on work orders. A simple quoted Google search of "atleast" will reveal 13,100,000 hits in .23 seconds. And clicking the news option after your Google search displays a whole hell of a lot of professionally written articles using that word. Most spell/grammar checkers won't even be of help. Now I am going to teach the easiest way to determine the proper grammatical usage of the two:
Atleast is not a word.
At is a word and least is also a word and the phrase "at least" is the only proper way to write them.