An investigation that CSO Online conducted has found that if you do not have your network-connected HDDs configured correctly, your files could be ending up in the wrong hands.
Their report stated that some personal cloud devices with external HDDs connected to routers with FTP enabled have been indexed by Google, which has seen personal files found on the Internet, and on search results. This includes very personal data such as emails, journal entries, passports, tax records, financial statements, mortgage documents, passwords, private photos and more.
The organization was able to map a family's personal and financial history all the way back to 2009 just by searching their name as their data was archived on a Western Digital HDD that they had connected through a Linksys WRT1900AC router. But when the family was warned about this, it was too late. The family noted: "I simply could not figure out how someone got the [card] info minutes after I'd activate them. My system was clean and secured more than the average person," said one member of the family. Now I know. [It's not] difficult when my backups were public and being indexed on Google".
CSO noted that other devices had been indexed, such as the Seagate Personal Cloud, Seagate Business NAS, Western Digital My Cloud and LaCie CloudBox. They have a detailed guide on how to check if your network-attached HDD is letting Google index it, which is something you should definitely check out.