Practically, you may be right--it may be very unlikely that you would be caught in your falsehood, for the reasons you indicate.Morally, you are aware of the problems.Legally, you need to be aware  that if it turns out that you are discovered by your friend's new employer, you could face substantial liability:1) If they would not have hired him but for your reference, you could be sued his wages to date, plus any training costs, benefits, etc.2) If he affirmatively causes harm--e.g. steals data or supplies, harms a client's business, resulting in liability to his employer, can't deliver on a contract, resulinting in lost wages, damages company property, commits some form of illegal discrimiantion or harassment (e.g. sexual harassment), etc.--and it surfaces that you lied to get him hired, you could potentially be sued for those costs or damages, too.