grammaticality - "Every" being used instead of "ever"?

Occasionally I'll see a comment on the internet along the lines of

I don't think I have every heard of such a thing.

Maybe not exactly that, but something equivalent where I would think that their use of every was 100% wrong, and ever should be used instead. It happens way more often than I would think, considering how much extra effort is needed to type the extra y and how dissimilar the two words are. Is it because

1. they are simply in the habit of typing "every" every time?


2. they actually have these words confused (how/why)?


3. they are all kids and most English speakers pass through this phase of misunderstanding?


4. they have all learned English as a second language, and either the words are equivalent in their native language, or there is a certain teaching style that doesn't make the distinction clear?


5. of some other reason I've failed to consider?