My friend JD Murray at Techexams.net has a nice definition of both, see his explanation below:
Oh, I hate these two. It’s like describing the difference between “jealously” and “envy.” Kinda the same thing but not exactly. Here it goes:
Due diligence is performing reasonable examination and research before committing to a course of action. Basically, “look before you leap.” In law, you would perform due diligence by researching the terms of a contract before signing it. The opposite of due diligence might be “haphazard” or “not doing your homework.”
Due care is performing the ongoing maintenance necessary to keep something in proper working order, or to abide by what is commonly expected in a situation. This is especially important if the due care situation exists because of a contract, regulation, or law. The opposite of due care is “negligence.”
In summary, Due Diligence is Identifying threats and risks while Due Care is Acting upon findings to mitigate risks
EXAM TIP: The Due Diligence refers to the steps taken to identify risks that exists within the environment. This is base on best practices, standards such as ISO 27001, ISO 17799, and other consensus. The first letter of the word Due and the word Diligence should remind you of this. The two letters are DD = Do Detect.
In the case of due care, it is the actions that you have taken (implementing, designing, enforcing, updating) to reduce the risks identified and keep them at an acceptable level. The same apply here, the first letters of the work Due and the work Care are DC. Which should remind you that DC = Do correct.
The other answers are only detractors and not valid.
Reference(s) used for this question: CISSP Study Guide, Syngress, By Eric Conrad, Page 419 HARRIS, Shon, All-In-One CISSP Certification Exam Guide Fifth Edition, McGraw-Hill, Page 49 and 110. and Corporate; (Isc)² (2010-04-20). Official (ISC)2 Guide to the CISSP CBK, Second Edition ((ISC)2 Press) (Kindle Locations 11494-11504). Taylor & Francis. Kindle Edition. and My friend JD Murray at Techexams.net