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Microsoft, once considered a stodgy software maker, has outperformed tech unicorns since 2015

Jordan Novet

Among private companies that were worth $1 billion or more in 2015, Twilio, Okta and Zscaler have produced some of the best returns. Taken as a group, they've underperformed a straight bet on Microsoft. In November 2015, tech investor Marc Andreessen weighed in on a hot debate about whether Silicon Valley's start-ups were frothy from all the cash propping up so-called unicorns, or venture-backed companies valued at $1 billion or more.