The two had alleged that Mark Zuckerberg, the current acknowledged owner of Facebook (inasmuch as anyone can own something with that many shareholders) stole their ideas in the early part of this century.
In 2008 they accepted the aforementioned sum in full and final settlement. Then earlier this year they resurfaced appealing that decision but failing because the judge ruled that they'd accepted a settlement, and only last week suggested they should have more yet again as there was new evidence.
This latest development appears to put the issue to rest permanently.
A deal's a deal
The two haven't given any reason for their sudden capitulation but it does look to me as an outsider that if you accept something in full and final settlement then it should be final. And full.
The American judiciary appears to have agreed, since the judge in the earlier case this year described the settlement as "favourable".