Required to return the money?

My friend worked for a large corporation until she quit in September \'06. Last week, she received a check (stub - she had direct deposit) for 600 hours pay. Not sure what to do, she called the local HR dept and told them about it. Today they called her back and told her to write them a check and mail it to their payroll dept which is in some third world country. My question(s) are 1) is she required to return the money? and 2) what happens to the $4900 already held for taxes and the extra income she might have to claim if the company doesn\'t undo their error correctly?

Yes she must return it--but normally sending abroad seems very odd...it sounds fraudulent and the check may be fake--what kind of company is this? Inform the police.