Bitcoins can be easily used to scam people out of their money due to the inability to perform charge-backs. What are the most notable cases of Bitcoin scams that are known?
Here's a list of the most notable scams, thefts, and hacks: https://bitcointalk.org/index.php?topic=83794
Here all famous scammers/sites:
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Welcome to Bitcoin.SE! Whilst this may theoretically answer the question, it would be preferable to include the essential parts of the answer here, and provide the link for reference. – Andrew Chow♦ Jan 24 at 0:39
If you look at a graph of the value of 1 bitcoin, that huge spike and drop was caused by someone hacking Mt.Gox and selling everyone's bitcoins to him/her for $0.00, dropping down the value to $0, and it stayed low as more people sold their bitcoins to make sure it wouldn't happen to them. It's been slowly rising since then.
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See #2 in this list: bitcoinmagazine.net/common-misconceptions-about-bitcoin-guide – Colin Dean Dec 31 '12 at 4:45