The deal will boost MyHeritage.com's user base by another seven million users to 72 million. Sacks will join the Israeli company's board of directors.
MyHeritage.com provides a host of family-oriented services, such as a social network and family tree research. Subscribers can keep in touch with distant family members. The company says that a user tracks 16 family members on average.
In an interview to the Wall Street Journal, MyHeritage.com CEO Gilad Japhet said: "When David Sacks started Geni in 2007 people have been telling me, ok, Gilad, game over. If a person of this caliber is moving into the space, your chances are slim. We were inspired from each other, and in the end David founded Yammer within Geni and spun it off. He was co-CEO of the two companies for two to three years.
Last year, the Israeli company acquired American FamilyLink.
This report was originally published in Hebrew by Calcalist