Level 33
...some quotes from the article above:

Improperly configured HDFS-based servers, mostly Hadoop installs, are exposing over five petabytes of information, according to John Matherly, founder of Shodan, a search engine for discovering Internet-connected devices.

The expert says he discovered 4,487 instances of HDFS-based servers available via public IP addresses and without authentication, which in total exposed over 5,120 TB of data.

According to Matherly, 47,820 MongoDB servers exposed only 25 TB of data. To put things in perspective, HDFS servers leak 200 times more data compared to MongoDB servers, which are ten times more prevalent. A report from Binary Edge from 2015 revealed that at the time, Redis, MongoDB, Memcached, and ElasticSearch servers put together exposed a tota of only 1.1 PB of data.

Most HDFS systems are located in the US and China
The countries that exposed the most HDFS instances are by far the US and China, but this should be of no surprise as these two countries host over 50% of all data centers in the world.

Earlier this year, attackers realized they could take over unprotected servers exposed online, steal their content, and demand a ransom. Attacks first targeted MongoDB, but they soon moved to CouchDB and Hadoop.