That means you got VAC banned, which can happen from any VAC-secure server(which is the majority of servers out there). When you used a cheat, anytime in the past, VAC logged it. It may not have banned you on-site, but will still ban you months after the cheating infraction.
I have no idea why they wait so long sometimes... but yes, they can and will ban you days, weeks, even months after you have stopped cheating and have rid it from your computer.
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