You cannot disable CTRL+ALT+DELETE that is a windows special key.
You cant disable ALT+F4 or ALT+TAB as those as also special keys.
You should not do that is my answer. That would definitely make me not visit that site again. Even if it's an internal site, disabling keys is a bad workaround to whatever problem you are having.
Short answer: You can't.
There are almost no good reasons to allow web pages to do that to a user, and a whole host of evil reasons. I'll give you the benifit of the doubt that you aren't trying to do something evil, but I can't imagine what that could be.
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