The intension is to make a small mount of money from the referral links while it still helps some users. However, I did it in a wrong way. Maybe we should did it like this:
1) Disable it by default.
2) Ask user's permission to enable it
3) Tell users why we add it.
"I mistakenly added a feature that would show our referral links to half a million users in their search results" isn't really believable.