When Nikil Viswanathan first saw the allegations rolling in on social media, he couldn't believe his eyes. Hundreds of people were accusing his app of being used for human trafficking and urging others to never download it.

Viswanathan is the cocreator of Down to Lunch, a simple meet-up app that has become wildly popular on college campuses. The app, which helps people spontaneously "lunch," "chill," or even "blaze" with friends, peaked at No. 2 on the iPhone download charts in the US in April (it has since settled into the 40-to-50 range).

The app's rapid rise to fame represents the Silicon Valley dream story. But a string of product woes and a bizarre social-media attack that branded the app a tool for people to kidnap teens show the double-edged sword of the internet "virality" driving today's tech boom.

The start

Stanford graduates Viswanathan and Joseph Lau built Down to Lunch last year to try to recreate the experience of living in their freshman-year dorms, where it seemed so easy to run into someone and get lunch, play basketball, or do whatever.

Viswanathan had tried five previous times to recreate this time of life (three times with Lau), but Down to Lunch was the one that finally started to stick, he tells Business Insider.

Here's how it works.

View photos Down to lunch interface More

The app lets you declare you are "down" for a specific activity — lunch for example — and then with a tap send a notification out to all your friends nearby. They can join the "event" if they are free, and then you can chat about the details. It's a way of spontaneously hanging out when everyone has busy schedules, Viswanathan says.

When Viswanathan began to work in tech after college, he noticed that he would constantly run into old friends and they would swap the refrain, "Hey, we should get lunch sometime." The problem was that "sometime" was in the nebulous future, and it would never actually get done. And when Viswanathan did have a free moment during work hours, he would start texting friends to see who else was free only to give up after a few "sorry, busy" rejections.

The theory behind Down to Lunch was that it might help Viswanathan actually have lunch with his non-work friends for a change.

The rise

After being released to the public about a year ago, the app started to pick up steam at colleges — starting at the University of Georgia.

At first, Viswanathan acknowledges, he was surprised. He and Lau had built the app in a day and hadn’t spent much time perfecting it.

"The product was barely functional," Viswanathan says bluntly. He acknowledges that even today the app can be a buggy mess. But college kids loved the concept, and even with its hobbled utility it spread to university after university. As their app gained popularity, the pair thought about stopping new users from joining. The two-man team was unprepared to scale the app and knew the product needed serious work. One of their advisers told them to just ride the wave, so they hired a small team to try to keep up and begin to improve it.

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