90% of altcoin users use wallet with one address and 80% of them use mult coin wallets and not single wallet.
are these percentages your own computation or are there any studies behind them?
i am curious because last time i checked majority of altcoin users were actually storing their altcoins on exchanges and don't have any wallets. it is also visible from their blockchain and lack of daily on chain transaction traffic.
I think that depends whether on the altcoin have real usage and availability of light wallet for that wallet.
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Not if you make request to all bitcoin transaction on bitcoin blockchain.
that would be impossible due to the gigantic number of transactions. and usually people check their own addresses or transactions only on a block explorer not other random transaction/address. so we can say that in majority of cases the block explorer can know with a high certainty that the request is made by the owner.
I totally forget number of Bitcoin transaction, but you still could :
1. Check it with Tor Browser to reduce privacy risks
2. Make request for your address and some random address (e.g. another output address of CoinJoin transaction)
I know it won't do not much, but it's better than nothing.