Paul D. Ceglia of Wellsville, N. Y., who is claiming half of the of Mark Zuckerberg's stake in Facebook, has filed an amended lawsuit by adding some emails that purportedly supports his claim.

Ceglia claims that the emails allegedly written by Facebook’s founder & CEO Zuckerberg to Ceglia in 2004 is strong evidence that show that Zuckerberg gave him 50 per cent ownership in Facebook for an investment in the then-startup company.

One of the alleged emails says, "According to our contract I owe you over 30% more of the business in late penalties which would give you over 80% of the company. I'd like to suggest that you drop the penalty completely and that we officially return to 50/50 ownership."

Responding to Ceglia’s claim, the world’s most popular social-networking site challenged the validity of the emails, describing the case as the “fraudulent lawsuit brought by a convicted felon.”

Commenting on the issue, Facebook spokesman Andrew Noyes said, "We believe this suit is completely frivolous, and we will fight it vigorously.”

Facebook, which has more than half a billion users, has been valued at more than $50 billion.