Reading what others have said (and judged) it's obvious that some people really don't understand what happens in these cases.
When I found out my ex-wife had had an affair with a mate of mine whilst I was in Iraq, I challanged her about it. She admitted to the affair, and agreed dates coincided with the conception of my son shortly after my return.
However, she wouldn't answer the question "Is there a chance my son is not mine?"
At this point she hung up, and refused to answer the phone. She left me hanging, whilst I was hundreds of miles away, turned her home and mobile off and refused to speak to me about it. I tried calling all night as I needed to know. My whole world had just crumbled and I was scared my son may be someone elses.
The following day I drove to my parents, and there was greeted by a PC, who was there to arrest me for harrassment. The ex had phoned the police and reported me. I also received a cautiion, and was told off-the-record that i was screwed simply on the basis that i'm a bloke. In the eyes of the law her story is given more credability because she is female, and more assistsance is given to her as she is now a victim of 'domestic abuse'!