I first heard about this "Mary Magdalene" conspiracy thing over 30 years ago, from some whackjob in Seattle who was convinced that the Gospels were all written by some Roman guy named Gaius Calpurnius Piso. I'll bet he is ticked that Dan Brown doesn't mention Piso even once in "The Da Vinci Code."
Dan Brown is also being sued for plagiarism from the authors of another book, "Holy Blood, Holy Grail" who claim that he ripped off their book.
Both wrong and old news.
I'm a professional writer so conversant with copyright laws.
So I followed the court case - in London. (I also read "Holy Blood, Holy Grail" some years ago.)
The authors did NOT sue Brown for "plagiarism" - they sued for 'stealing ideas'. This, as anyone in the business knows, is bogus. Ideas cannot be copyrighted - exactly the judgment of the judge. (If ideas could be copyrighted, the libraries and book stores would be pretty empty as only one book could be written on any given subject.)
Two things ridiculous about Leigh and Baigant's suit: the 'ideas' in Brown's book have been written about for hundreds of years - including many contemporary books also currently in print - so they could hardly lay claim to the ideas as theirs in the first place.
They also had to know that ideas cannot be copyrighted, but I suspicion they hoped to get a judge that would wink at the law and thus ban further sales of the book and the movie.
(They also may have been a bit jealous of Brown's level of success over theirs)
They lost their shirts.