Why are some of us willing to share the boring details of our lives — from vacation logs to the minutiae of workplace dramas — online while others are content with keeping a low profile?

It has everything to do with personality, according to a recent study by MasterCard that found that traditional demographics such as age, gender and race are poor indicators of individual attitudes toward online privacy.

More important is what is motivating a person’s online activity, said Theodore Iacobuzio, MasterCard’s vice president of “global insights.”

To understand how consumers are using the Web, MasterCard conducted interviews with about 9,000 Internet users around the world.

“We were blown away,” Iacobuzio said. “No demographic characteristic achieves primary importance here. It’s all about why you go online. Why you go on determines your attitude toward data privacy.”

Based on MasterCard’s research, Iacobuzio and his team defined five privacy online personality types: passive users, proactive protectors, solely shoppers, open sharers and simply interactors.

As one might guess from the categories, the privacy personas are defined by online activities, such as shopping or social networking. “Open sharers,” for example, are happy to share information about themselves to get value back, whether it’s publicly checking in to a business to get a deal or simply saving their shipping information on an online site for convenience.

“Proactive protectors,” however, are less willing to share information with marketers and less active on social networks. People who fall into this category tend to have been burned by security breaches or other unexpected online outcomes, the report found.

Still, attitudes toward privacy don’t necessarily fall along a neat spectrum, Iacobuzio said. For example, people who primarily shop online might be happy to share information with merchants to get a good deal but might not be as open on social networks.

“It’s not the Goldilocks thing,” he said. “Your attitude will determine your behavior.”

Personality types are unlikely to change, he said. It’s unlikely that someone will start out as a proactive protector and turn into a open sharer.

The findings indicate that consumers are much savvier about online privacy than many people believe, he said.

“One of the real lessons of this piece is that consumers are well aware of how to protect [their privacy] and whether they want to or not,” Iacobuzio said. “Some of them are willing to trade information to get some benefit in return.”

For merchants, he said, there’s also value in identifying certain types of people based on their activity, such as “open sharers” or “solely shoppers.” Those two personality types make up about 40 percent of all online shoppers, he said, and if companies can identify those users, they can make their ads more focused and efficient.

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