Do you know what your kids are doing online? A new study shows you probably don't.

According to research by Webroot Software, what parents think their kids are doing online and what kids say they're doing online are often two different things.

"Without proper parental guidance, children can put themselves at risk, compromise valuable family information, or be the sources of bad behavior like illegally downloading videos or music or bullying," said Mike Irwin, COO of Webroot Software, in a statement. "The good news here is that these potential problems can be largely avoided if parents apply the same vigilance to the online world as in the offline world. Direct and ongoing conversations with our kids, and establishing guidelines with the help of the right technology, will go a long way in supporting good judgment."

More than 70% of the surveyed children, ages 11 to 17, said their parents ask them about their online activities, but they may not be getting accurate answers.

According to Webroot, more than half of the teens surveyed said they buy things online, but 71% of parents said their children never buy anything over the Internet. Forty percent of the kids said they use instant messaging and social networking websites, like MySpace and Facebook everyday, while only 30% of the parents said their children participate in these sites. And 45% of the kids say they spend an average of three or more hours on the Internet a day but 76% of parents polled said their children spend an average of two hours or less on the Internet.

The survey also supported concerns about the online risks that children and teenagers face.

Forty-three percent of teens who use social networking sites said a stranger invited them to meet within the past year. At the same time, nearly 40% of children ages 11 to 17 reported receiving a sexually explicit e-mail or pop-up advertisement within the past year. Nearly 100% of the children surveyed said they use e-mail.