Verizon Wireless has been subtly altering the web traffic of its wireless customers for the past two years, inserting a string of about 50 letters, numbers, and characters into data flowing between these customers and the websites they visit.
SAN FRANCISCO — Bob Foreman’s architecture firm ran up a $166,000 phone bill in a single weekend last March. But neither Mr. Foreman nor anyone else at his seven-person company was in the office at the time. “I thought: ‘This is crazy. It must be a mistake,’ ” Mr. Foreman said.