The New York Times killed a story which connected Acorn and the Obama Campaign in questionable activities, some of which would have violated election laws. It would have made an “independent expenditure” an arm of the Obama Campaign, which would be illegal.
Also, there may have been evidence that the Obama Campaign was making use of the strong arm tactics which Acorn is known for. That is their form of community organizing, after all.
There has been testimony before the House Judiciary attesting to this which was convincing enough that John Conyers (D) of Michigan and a very liberal representative as ordered a full investigation. Obviously the Times killed the story to avoid hurting Obama’s election chances.