Penetration testing: IT professionals demonstrate how hackers can access webcams
3 June 2013 Last updated at 00:02 BST
Many users of the internet think that by not replying to 'phishing scams' - false invitations encouraging you to hand over personal information - they are safe online.
But hackers use increasingly sophisticated techniques to trick more savvy web users, and gain control of their computers.
The BBC's LJ Rich visited the Swedish security firm Sentor in Stockholm, who carry out professional 'penetration tests' for companies to see how strong their cyber defences are.
Analyst Bjorn Johansson demonstrated to her how internet users can give hackers control of their computer, including the webcam, just by visiting a vulnerable web page with an internet browser.
Video Journalist: Dougal Shaw