I haven't used my MultiBit wallet in years. Now, when I try to access my Bitcoin, I run into some issues.
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First you state it's your own MultiBit wallet not being in use for years.
It appears I encountered a phishing website. The wallets definitely weren't intended for me. Someone sent me recovery phrases and a website address to supposedly recover their bitcoins. Fortunately, I tested it on a computer that doesn't contain any sensitive data, so there shouldn't be any issues.
Interesting, now it's someone else's wallet who gave you all their wallet's secret and YOU compromised that wallet and likely your own laptop (your laptop is recoverable, the wallet's content likely not anymore). You don't do any prior research, willingly handing over recovery words on an online website which is per se a total no-go with mnemonic recovery words???
I assume that your "someone's" wallet is now drained. How do you want to explain this to your someone? I'm curious!
Seriously, you shouldn't offer recovery services if you're not professional at all and what you did was the opposite of professional action.