Infowar: strike early, strike often:

The Washington Post has a timely article about the psychology of believing news reports, even when they've been retracted - suggesting that if false information is presented early, it is more likely to be believed, while subsequent attempts to correct the information may, in fact, strengthen the false impression.

Negating a statement seems just to emphasise the initial point. The additional correction seems to get lost amid the noise.

One particularly pertinent study [pdf] not mentioned in the article, looked at the effect of retractions of false news reports made during the 2003 Iraq War on American, German and Australian participants.

The study found that the American participants' belief in the truth of an initial news report was not affected by knowledge of its subsequent retraction.

In contrast, knowing about a retraction was likely to significantly reduce belief in the initial report for Germans and Australians.