John Loftis, at his blog Debunking Christianity, lists ten objections, concepts, or topics that seem to be raised most often by atheists in debates with theists. Here's the fifth (my response to the earlier objections can be found by scrolling down the page):
5. The problem of miracles is a serious challenge that must be overcome for any testimony or private revelation of the divine to be taken as veridical.
The meaning of the writer is unclear, but I take him to be saying that if miracles are to be cited as evidence that Christianity is true, the arguments against miracles must be persuasively answered. Well, they have been.
Historically, the strongest argument against miracles is David Hume's essay in his Inquiry Concerning Human Understanding where he states that 1) even if the evidence for a miracle were very strong it's cancelled by the stronger evidence of our uniform experience that the laws of nature are never violated, and 2) the evidence for a miracle can never be very strong in any case. Both of these claims have been refuted by modern philosophers, both theistic and atheistic.
To take just two responses, of the many that philosophers have adduced against Hume, consider the following:
Hume's first point fails to take into consideration the fact that the improbability of a law of nature having been violated can be easily cancelled out by the improbability of the evidence for a miraculous event existing if the event did not in fact occur (see Topic #1).
Moreover, laws of nature only apply to closed systems. Thus, Hume's argument assumes the world to be a closed system, i.e. that there is no God or that God never intervenes in the world, but this, of course, begs the question. If God does not exist then miracles are indeed highly unlikely, but why assume that God doesn't exist?
Against his second point it could be said that we can only know how strong the evidence for a given instance of alleged miracle is by examining that evidence. We can't assess the strength of the evidence apriori, much less assert apriori that no amount of evidence would warrant believing that a miracle had occurred, unless we've already concluded that miracles are impossible.
But this, of course, would also beg the question.