Confounding Factor is:
Confounding factor:

One which is associated with BOTH exposure and disease and is distributed UNEQUALLY in study and control group.
It is itself a RISK FACTOR for the disease. 
e.g. – study of coffee drinking and lung cancer – if coffee drinker is also a cigarette smoker then this cigarette smoking is a confounding factor. Confounding factor can be neutralized by MATCHING
Itself a risk factor for the disease.
Associated with both exposure and disease.
Is distributed unequally in study and control group.
All of the above.