Before NSO helped the Saudi government track its adversaries outside the kingdom, and helped the Mexican government hunt drug kingpins, and earned hundreds of millions of dollars working for dozens of countries on six continents, the company consisted of two high school friends in northern Israel with one relatively mundane idea.

Using technology developed by graduates of Intelligence Unit 8200 — Israel’s equivalent of the N.S.A.— Shalev Hulio and Omri Lavie started a company in 2008 that allowed cellphone firms to gain remote access to their customers’ devices to perform maintenance.

Word spread to Western spy services, whose operatives spotted an opportunity.