Yes you can just say that.
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If someone knows for a fact that you have Monero and they know the exact amount, and want to know where it came from:
- Move them to a new wallet
- I mined these coins a very long time ago, I do not have the mining equipment anymore
- Also the wallet I used to mine them was on an old computer that got infected so I moved all to this new wallet
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If someone suspects that you have Monero but does NOT know how much:
- Imagine you own $10k in Monero
- Move a small amount to a wallet ($200??)
- If authorities ask you how much you have, show them the wallet with $200.
- Go back to scenario 1 (I got those 200 from mining a long time ago etc etc)
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If no one suspects that you have Monero, and for now you are "in the clear":
- Follow good opsec
- Do not tell anyone that you have Monero
- Do not exchange that Monero for fiat using KYC services. Always use something like Haveno, or use the Monero to buy prepaid cards anonymously to use in shops
- If someone starts suspecting that you might be using Monero but does not know how much, revert to scenario 2
Of course it is better if you avoid anyone knowing you have Monero altogether.
Remember that you always have the option of moving them to a new wallet, say you got hacked and have no access to it.
Of course all this depends on your country and how authorities are there. If you live in a very authoritarian area where authorities do not care about evidence and they only care that "you look guilty", nothing will save you. If you live in a country where you must go to court and be proven guilty, I think with Monero its pretty easy to do any of those steps and cover your ass.
But as always, try to not be discovered using Monero in the first place
They add support for USDT I assume, as there is no support yet. Weird wording I agree