"I think the creators of Craigslist had no intent of harming society. They came in with good intentions. At the same time, they did not anticipate the different ways users could use the features in an unexpected way with unintended consequences."

Websites like Craigslist have exploded in popularity by creating a community where it’s easier than ever for members to meet, share information, and buy and sell goods. But the technology that facilitates these connections may be wreaking devastating, unforeseen havoc on society.

Assistant Professor Jason Chan first became interested in the unintended consequences of the internet while, ironically, surfing it. A news story featuring doctors’ reports that patients were contracting STDs through online encounters caught his attention and got Chan wondering whether these were just anecdotes or evidence of an online phenomenon.

Craigslist provided him with a unique testing ground to find out. Because the introduction of Craigslist into each new market is random with respect to HIV trends, Chan could determine the connection between the entry of Craigslist and the rate of new HIV cases.

According to Chan’s research, the entry of Craigslist into a market resulted in a 16 percent increase in HIV cases. When mapped at the national level, more than 6,000 annual cases and $65 million in related treatment costs can be linked to the website.

Through rigorous analysis and sub-checks, Chan and his colleague determined that the positive link between Craigslist and HIV trends stemmed from users who frequented the popular “personals” sections, and not from the areas of the site used by sex workers.

“The study results suggests that there is a new social route of HIV transmission that is taking place in the digital era,” says Chan. “Healthcare practitioners and policymakers have to look more closely at online platforms for the way HIV and STDs can spread across the country.”

The Centers for Disease Control and Prevention has already taken note and posted an earlier version of Chan’s research on its website.

Watch Chan describe his findings

“Internet’s Dirty Secret: Assessing the Impact of Online Intermediaries on HIV Transmission” Chan, J., Ghose, A., MIS Quarterly (Dec. 2014)