He ran five servers on IPv4-only addresses, while the other five ran only on IPv6 addresses.
The root password of both the servers was set to password, which is strictly avoided in production environments.
The hackers took only 20 seconds to brute-force the SSH root account.
However, on the other hand, the IPv6 servers had much better results.
However, that was not the end of the SSH brute force experiment.
Source:Sucuri Blog
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source: www.techworm.net