What are sensitive files or information?
Sensitive files or sensitive information is all your files, that you decide not to share publicly with the world. These files, among others, contain business critical pieces of information (like business plans, marketing strategies, etc); business niche expertise gathered throughout the years; paid content (like pay per - view, download, listen, read); sensitive customer information; promotional, proposal or bidding documentation; etc. These files should be always under a lockdown and accessible only by a few, within your company.
What is information leakage?
Sensitive files are stored online, with the rest of your files. When these files can be accessed publicly, it can be downloaded, read and shared by anybody. It is not hacking (or stealing) since you're technically sharing these files. If you own sensitive information, chances are, that you are sharing them publicly - it is only a matter of knowing how to reach them.
Is this happening in real life? Oh, yes!
Even with big business entities, who afford to employ top-notch intellectuals and specialists. Read about this news here from August 09, 2017. "An anti-malware detection service provider and premium security firm has been accused of leaking terabytes of confidential data from several Fortune 1000 companies, including customer credentials, financial records, network intelligence and other sensitive data. However, in response to the accusations, the security firm confirmed that they are not pulling sensitive files from its customers; instead, it's up to companies—who are accidentally (but explicitly) sharing their sensitive data to leverage an optional cloud-based antimalware service."