Sorry to say but even if this person learn how to sign a message is the BTC coming back? Are you guys going to get his BTC back for him? Why are you forcing him to sign a message? So that you can believe that he is indeed the rightful owner? What is next after? Let us send his BTC back to him since he is the rightful owner?

OP, I am glad you learned your lesson, you don't have to keep longing this thread, you shared your pain and people don't still believe, leave the post and move on, new readers will learn something from it or also join the group of people that don't believe.

My advice for you now is to get a hardware wallet, it's not even up to $300 to get a solid one, Trezor, Onekey, Keystone, Tangem, D'cent, and so on, these wallets are badass, good for keeping large amount of crypto, now they are doing discount, black Friday's everywhere, act now to avoid future losses, take heart and be strong.

Why do you think mods are reading this? Even if they read, first someone should make a report so that something might happen - and if you think the topic should be closed, why don't you click on the "report to moderator" button in the OP?

11 BTC? Damn. That's a lot of money for people like me and I must say that you are handling this really, really well since losing that amount would most probably shake me to the core.

If you weren't using that amount actively for various purposes, I must say that it was pretty dumb of you to leave it in an online wallet as some of the posters above mentioned. All the best trying to recover your stash.

You are absolutely right in this statement. But that doesn't mean my assumption is wrong.

And if you are finished, then I hope you don’t mind me expressing my vision of the situation in more detail?:

I believe that OP did not lose any bitcoins. I propose OP simply made up this sad story so that out of pity or solidarity they would pour him merits. He didn't succeed. I’m glad that the forum’s audience is getting smarter every year and is less and less susceptible to such provocations

I also do not exclude other theories, the proposal of Pmalek also makes sense:
https://bt.irlbtc.com/view/5475428.msg63217689#msg63217689

Is such a free interpretation suitable for a report? I thought the report should be short. It turns out there is no single standard form for reports? Please do not evade away from newbie answers and provide at least a sample of a correct report

Yesterday I lost 11 BTC from my Bitcoin Core 25.0 wallet.  The wallet wasn't open at the time.  I don't know how it happened. Lots of emotions right now.  

edit to add:

Definitely not my wife. We live in a rural setting. She doesn't have the computer knowledge to even launch the wallet. This was an external hack.

I first noticed when I logged into Koinly and saw my BTC balance was reduced.  I then launched Bitcoin Core and it was about a week behind.  Showed my 11btc as it updated, then hit the date of the hack and it went to zero.  Wallet is encrypted and appears to work fine. PC is turned off now and hard drives will be wiped. This definitely sucks, but not the end of the world.  Opportunity for others to learn or be reminded from my mistakes.

Also, the coins have not moved from hacker address.   After further investigation this looks to have been caused by a botnet.

edit 2:

All of my addresses in Bitcoin Core are segwit.  I can't seem to find a way to create a signed message with segwit and Bitcoin Core.  If you don't believe my post that's fine.  I'm not looking to gain anything, just want to tell my story so others don't make the mistakes I did.

TX IDs of the four transactions that drained my wallet:

e4fda9c61c782ad0035ee9b5c551e7e48a67c294499ae7cdc6702c7d3b06b19e

1ec109e71874990c33afd66eff4050776a1ba796d92b97cea8dc48b948fed6c8

95e9e7a88536668bbfaaf12b417ec3ec74d851d018726511ec797061d495c97a

ed8e7988e4c000b05c1814c3aaeb5170a452ee54c2dd33cc1e533fbc885ec25d

Yesterday I lost 11 BTC from my Bitcoin Core 25.0 wallet.  The wallet wasn't open at the time.  I don't know how it happened. Lots of emotions right now.  

Because it's quite often for newer members to come up with such stories to attract attention and merit as well, in a desperate attempt to rank up. I don't know what to believe. I've read a whole lot of stories here, and a large number of them were fiction. I can't accept that someone who supposedly had 11 BTC, worth approximately half a million dollars, was that of a novice who did not have a hardware wallet, which barely costs $70, and kept his wallet on a shared Windows computer, not even a separate computer or OS for this purpose. I'm sorry, but it doesn't sound plausible.