What happens when you leave a database filled with personal information open to the Internet? People find it: That's what happened to marketing data firm Exactis with its database of information on roughly 340 million people.

Security researcher Vinnie Troia of Night Lion Security discovered the database through a Shodan search. Exactis is a marketing data company that provides companies with the sort of information needed to target ads to people browsing the Web.

Troia told Wired, "It seems like this is a database with pretty much every US citizen in it," adding, "I don't know where the data is coming from, but it's one of the most comprehensive collections I've ever seen."

While the data did not include credit card or social security numbers, it did include everything from political preferences to browsing and purchase data for a wide variety of items. Taken together, the pieces of information would allow an advertiser or database user to form a very detailed picture of the targeted individual.

"The data reported to have been leaked is incredibly comprehensive and can be used by hackers to develop more targeted phishing scams," said John "Lex" Robinson, cybersecurity strategist at Cofense. "Phishing is a serious threat because it works, with personalized phish often making their way past stacks of expensive technology layers and email gateways to land in an unsuspecting user's inbox."

In terms of size, the Exactis leak dwarfs the Equifax breach, which exposed nearly 146 million records. Exactis has now taken the database off the public Internet, but has made no public statement on the affair. At the time of this article's publication, the company's website was down, with a request returning a 508 error.

For more, read here and here.