I retraced hacker's transfers and I realized that he swapped all crypto to usdt and transferred all to okx exchange.
Do you think there's a possibility to freeze hackers okx account or something ?
It is possible, depending on the situation at hand it may be even likely to have them frozen. However, this does not mean they can do much about it particularly because this is a situation that Authorities have to work on and not the Exchange itself. Do not lose hope, but be realistic about the situation. This is a theft that may or may have not been well planned. If they did not Withdraw your brothers Cryptocurrencies to their Bank Account or if they did not complete Know Your Customer procedures, chances are dimnished.
I am mind blown how some people do not have at least a Hardware Wallet and prefer to rather hold this much Money on a Computer they do not even properly secure. I do not want to carve the knife even more against his skin but why? This was a constantly open invitation for any bad actor to his Wallet!
Whether he gets Authorities to retrieve his Money or not, from this extremely expensive lesson he must learn a thing or two. Do NOT Trust your Computer and NEVER should you consider it is a safe idea to browse dubious websites or to open Email attachments on the same Computer you have very sensitive information on! An old Computer can be purchased from about 20 Dollars and above and you can turn it into an Airgapped Device just perfect for storing Cryptocurrencies safely. Or, just purchase a Hardware Wallet instead. For 100 THOUSAND Dollars this should be a must!
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This is all too common these days these hackers are getting smarter with social engineering and AI,
What does Artificial Intelligence have to do with what happened to OP? They simply opened an infected attachment. This is one type of Hacking that has been around for many years. Long before AI was at the tip of our tongue.
I like to use browserling which is like a browser VM that allows you to check in a safe environment before compromising your own.
OP, do NOT follow this idea. NO! A 'Browser VM' does about NOTHING to protect you from an infection if the Virus is intelligent enough. If you really feel the need to open unknown Files, DO NOT OPEN THEM ON THE COMPUTER YOU STORE BITCOIN ON.
I have never been infected from Email attachments. Not even once because I simply do not click what I know is not legitimate or something I should of received! Is it this difficult?