I applied for internships at companies A and B.
Company A offered me an internship and company B offered me an interview. I decided to accept company A's offer and email company B to let them know that I was withdrawing my application due to accepting an offer elsewhere.
Company B has replied to my email asking me where I accepted an offer, should I tell them?
Company B has replied to my email asking me where I accepted an offer, should I tell them?
There's no benefit to you from informing Company B of where you will be employed.
While it's unlikely to have any adverse affect either, there's a small possibility that someone at Company B will try to undermine your acceptance (call company A and say bad things about you, for example). I personally don't know a case where that has actually happened, but I've heard stories.
There's probably nothing nefarious going on here. Company B probably just wants to stay in touch. But after you are happily settled in your new position, you could reach out and contact them if you choose, with no risk.
For now, I think just letting Company B know you have accepted another offer, thanking them for their time, and wishing them continued success is the most prudent course of action. That's what I've always done in similar circumstances.
Company B has replied to my email asking me where I accepted an offer, should I tell them?
That's entirely up to you. You have no obligation to tell them and they have no right to insist on you disclosing. If they're really that curious they can wait for your LinkedIn status update to find out anyway.
If you think it's possible that you'll apply with them again at some point in the future then it can be beneficial to inform them, but not all hiring managers or HR staff will remember that kindness or still be around if you apply again. If I had established great rapport with the hiring manager at Company A and seriously considered their offer then I would be honest about my reasons for rejecting it.
As an anecdote, I was once in the running with 4 companies:
Joe mentions the potential risk that Company A might try to sabotage your offer at Company B but no professionally-run company will do that just as they wouldn't give any thought to such bizarre attempts at character assassination.
Ask someone at Company A for their advice. It may be common in this particular industry for HR departments to track where and why're they're losing intern candidates.
This way, your company knows that the other company (B) also wanted to hire you and anything negative they could say about you would make them look foolish.
