It was happened also this thing :
Hello,
there has been a lot of reused R values in the signatures on the blockchain, recently. This exposed many private keys. After googleing the addresses, I think it is related to Counterparty (XCP). Here is a list of the exposed addresses in alphabetic order. Most keys were exposed very recently, i.e., in the last week.
If you own one of the following addresses, you should transfer the money to a fresh address (before someone else does it for you). Also figure out, which client has the bug that revealed the private key by reusing R values. Then notify the author of that tool.
....
It "was not related" with the bitcoin code itselft but with a bad generation of the private key (and address).
This is an interesting article (about that situation) :
Upon running the script last Monday morning, he said he recognized immediately that it had found something. The script, which had discovered only about 500 such 'broken' keys in the bitcoin blockchain's five-year history, had suddenly unveiled 500 more in a single day. A second script he wrote scanned the public ledger to see if any funds had been sent to those addresses, and was startled to see the amount. "I had prepared some scripts to assist finding and spending the money from the broken addresses, but I hadn't prepared it for this scale." He sorted the transactions, starting with the most valuable ones and sweeping the funds from the broken addresses into one he controlled. The scripts prepared and signed the transactions, double-checking for correctness and transaction fees, about one every two or three minutes. Some, such as freshly mined bitcoins that can only be spent after 100 confirmations, took longer.
http://www.coindesk.com/good-samaritan-blockchain-hacker-returned-255-btc-speaks/ 
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