Google has been working on a top secret project with a leading healthcare company to gather millions of Americans' health data without them knowing it. 

The Wall Street Journal first reported on Monday that the company has teamed up with Ascension, the second largest healthcare services company in the country, for a project that was being code-named Nightingale. 

Within hours of the Journal's report, the two companies announced the collaboration in a press release where they revealed that Ascension's data will move onto Google's Cloud platform.  

Google will now have access to patients' test results, diagnoses and hospitalizations to give them a full digital health history. 

Neither doctors nor the patients in the 21 states where it will be used had been told about it.