My considered comments are: -
1. When an interviewing ageney/ company, seeks , proprietary/ confidential details, they are being unprofessional.albeit inapprpriate, as such, should not be obliged.
2. Any smart move of this type, can only be a short term objective, and unlokely to sustain.
3. Do, Head Hunters not have principles?
4. For Pankaj Only Carry this as an experience to learn from. It is very clear, that the experience was unpalatable, and can be nauseating, particularly to one unsuspecting. Make sure you do not do such an injustice to any one, and use this experience at later stages to bring good points home to the others.
Pradeep