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It's scary how much each candidate in the upcoming midterm elections knows about you. And it's all information you've willingly given up over time.

The trove of data goes beyond voter registration information like your name, home address and date of birth. Thanks to an army of data crunchers who marry that information with data you drop at a clothing or automobile site, many candidates often have intimate knowledge of who you are and whether you're likely to support them. 

The increasingly effective use of big data to create targeted political ads is one of the main causes for the climbing costs of running a campaign.

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Facebook's data scandal involving consultancy Cambridge Analytica shed light on how companies can take personal information we give away and transform it into highly effective targeted ads. Data was used to help sway the 2016 US presidential elections, one of the most dramatic examples of a practice that's been around for much longer.

While you may be aware your data is being used, you might not know the full extent of the process. So we dug in to find out how data goes from your voter registration form to data brokers and back to you in the form of a political ad. 

You start giving away personal information when you register to vote. 

That information is added to a database each state keeps, thanks to the Help America Vote Act. The legislation required states to maintain centralized, computerized voter registration databases to help election administrations keep track of eligible voters. 

In some states, the information can be obtained free. Other states charge, with fees ranging from $2.50 in Arkansas to $30,250 in Alabama. The data includes, at a minimum, your full name, address, voting history and jurisdiction. Some states, such as Florida and Texas, include more information, like date of birth, phone number or race.

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All states allow access to voter data for election purposes, which usually lets political campaigns request voter files from state authorities. Companies can also request the information, if it's being used for political purposes. 

Campaign software companies, like NationBuilder, turn to state offices to keep their voter files updated. 

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The rules differ when it comes to uses of voter data for purposes other than elections. California, New York, Nebraska and others have specific laws limiting who can access the data and what it can be used for. Many states don't allow commercial use of voter information. Vermont specifically prohibits sharing voter data with foreign governments and agencies. 

However, Alabama, Alaska, Florida and some others have no restrictions. Anyone can request the data for any purpose. 

Voter information alone, however, isn't that helpful. That's where data brokers come in. 

You've probably heard of the term Big Data, the ability to make sense of huge amounts of data. Data brokers do that when they link your voter information to information you've submitted on retail sites. That isn't hard, because the personal information you provide for voter registration is likely the same as what you give to online merchants. This enables data brokers to match your purchases, your house and your car to you.

Consumer data comprises all sorts of odds and ends of varied importance, including property ownership, marital status, wealth and income, all of which provide a high-level picture of you. It can also include magazine subscriptions, club memberships and other granular information that gives a sense of your interests. 

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Sometimes voter information gets leaked online. 

Earlier this month, researchers found hackers selling 35 million voter records from 19 states on the dark web, according to a report from Anomali Labs. The hackers charged between $150 and $12,500 for statewide voter lists. 

In July, Virginia-based political campaign and robocalling company RoboCent left hundreds of thousands of voter records online without protection, according to ZDNet. A RoboCent spokesperson told CNET in July that the company partners with data firms NationBuilder, Aristotle and i360 for voter data. 

"The very politicians who fight for consumer data are also using it and not responsible for [where] that data goes to after campaigns," said Kim Alexander, founder and president of California Voter Foundation. "If the government collects all this info on people, they need to protect it." (Full story)