I know there are probably hundreds of threads on this subject, here is one more.
Somebody messaged me about a coin and mentioned that they have a significant amount of a coin in a wallet that is online so I'm just making a generic post to explain the problem a little and maybe somebody else who understands better will improve or link to a better post on the subject.
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When you put coins in a wallet, and that wallet is on a computer that is connected to the internet, you have a very high chance of losing those coins eventually. It may take a week, a month, a year, ten years, but eventually the coins will be gone.
Hackers are getting more and more slick with coins and crypto is probably the most attractive new target to hackers online.
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The best solution, which does not even protect you 100%, is to have a dedicated offline computer, a computer that never touches the internet, and create wallets on it.
When the wallet has never touched the internet the chances of a hacker getting to it are slim, but still not zero.
Why is there still risk, even if you create a wallet offline? Among other things, there are downloaded wallets that are dirty. Your browser could be redirected to download a wallet that was modified in such a way that any addresses it creates are compromised.
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There are so many people who have had coins hacked, many of them knowledgeable people, that if you are a new person just getting into crypto you can probably expect to get hacked before too long.
https://www.bitcoinarmory.com/tutorials/armory-advanced-features/offline-wallets/https://en.bitcoin.it/wiki/Cold_storage-----
Online wallets and exchanges get hacked very frequently too.
https://www.reddit.com/r/Bitcoin/comments/4opoy3/coinbase_and_gmail_accounts_hacked_from/https://bitcointalk.org/index.php?topic=1516588.0https://www.reddit.com/r/Bitcoin/comments/3ibh95/coins_stolen_from_mycelium_wallet_how_do_you/https://www.reddit.com/r/BitcoinMarkets/comments/3e85rc/my_bitfinex_account_was_hacked_and_all_my_money/https://talk.paxful.com/t/bitcoins-disappeared-to-an-unknown-bitcoin-address/1674https://bitcointalk.org/index.php?topic=1423584.0https://bitcointalk.org/index.php?topic=951151.0https://bitcointalk.org/index.php?topic=875805.0https://www.reddit.com/r/Bitcoin/comments/42tp55/coinbase_with_2fa_and_emailsms_alerts_hacked/and on and on