Okay, but that’s not what was being asked. OP, someone who presumably understands the difference between a totally invalid cert and an expired one, was asking specifically whether clicking through the latter is dangerous.

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axus 4 hours ago | parent [-]

"Visitors to the site are vulnerable to Man in the Middle (MitM) attacks, IF they click past the warning". I think it's true when there is a man in the middle.

	▲	fylo 3 hours ago \| parent [-]
		Based on history of this type of attack, it can also be true with a valid certificate ;)