The term “paternity fraud” is used to describe any instance in which a woman lies about the paternity of her offspring. She might use the lie as a means of providing a fatherless child with a "father-figure", or she could might use it to extract money from the man she falsely accused by filing for child support maintenance.
Under the Family Law Act 1975 - SECT 69Q, any child that is conceived by a woman while she is cohabiting with a man is presumed to be his child. 
FAMILY LAW ACT 1975 - SECT 69Q
Presumption of paternity arising from cohabitation
(a) a child is born to a woman; and
(b) at any time during the period beginning not earlier than 44 weeks and ending not less than 20 weeks before the birth, the woman cohabited with a man to whom she was not married;
the child is presumed to be a child of the man.
Under SECT 69T of the same act, a man is presumed to be the father of a child after he has provided an instrument [of law] acknowledging that he is the father of the child. The instrument of law is a legal document that has the man's signature written underneath a caption of text that declares him the father of the specified child. 
FAMILY LAW ACT 1975 - SECT 69T
Presumption of paternity arising from acknowledgments
(a) under the law of the Commonwealth or of a State, Territory or prescribed overseas jurisdiction, a man has executed an instrument acknowledging that he is the father of a specified child; and
(b) the instrument has not been annulled or otherwise set aside;
the man is presumed to be the father of the child."
In either of the aforementioned cases, the man is viewed as the legal father of the specified child -- even if it is later discovered via the usage of DNA Testing that he is not the biological father. Only a court order can revoke the man's legal status as the child's legal father. Without a court order, the state can -- and has done so in the past -- overlook the DNA evidence and order the man to financially support the specified child.
In the United States of America (USA), most jurisdictions are descended from Old English Law, and uphold a 500-year-old English Common law doctrine that does not acknowledge paternity fraud as a crime. A dozen or so states in the US are amending legislation on this issue.  
Commonwealth Consolidated Acts FAMILY LAW ACT 1975 - SECT 69Q Australasian Legal Information Institute (AustLII), Sydney, New South Wales. [AustLII webpage for article]
Commonwealth Consolidated Acts FAMILY LAW ACT 1975 - SECT 69T Australasian Legal Information Institute (AustLII), Sydney, New South Wales. [AustLII webpage for article]
Tresa Baldas Parent Trap? Litigation Explodes Over Paternity Fraud The National Law Journal. 10 Aug 2006. [NLJ webpage for article]
Natural Selection in Family Law: Legal Cases and Materials 3.2. Marriage and the Paternity Presumption Biojuris [Biojuris webpage for article]
THE STATUS OF MEN IN NEW HAMPSHIRE FIRST BIENNIAL REPORT OF THE NEW HAMPSHIRE COMMISSION ON THE STATUS OF MEN Commission on the Status of Men (New Hampshire Government), 1 Nov 2005. [CSM webpage for article]