Brace yourself for a tidal wave of Facebook campaigning before November’s U.S. presidential election. A study of 61 million Facebook users finds that using online social networks to urge people to vote has a much stronger effect on their voting behavior than spamming them with information via television ads or phone calls, Science Now reports.

The study follows a Science paper that tracked how people influence each other’s online behavior through Facebook.

On Election Day, about 60 million people received a message that encouraged them to vote. It included links to local polling stations, a clickable “I Voted” button, and photos of six of their randomly chosen friends who had already clicked the “I Voted” button.

The photos apparently worked: People who received messages alerting them that their friends had voted were 0.39% more likely to vote than those who received messages with no social information. That translates to an additional 282,000 votes cast, the team reports online today in Nature.