The YouTube videos you watch can be tracked

Gaps in YouTube's encryption enable both government intelligence agencies, hackers and internet marketers to determine which videos a user is watching, said the researchers.

"We built a simple yet robust machine-learning algorithm that can identify which video you watched -- within a predetermined set of videos -- with a high degree of accuracy," said one of the researchers Ran Dubin from Ben-Gurion University of the Negev (BGU) in Israel.

"The algorithm is based on an in-depth study of how video services work, how video content is encoded and how a video player requests information to play it," Dubin said.

Dubin was able to use this algorithm to determine if someone had watched a specific video from a set of suspicious, terror-related videos. 

Intelligence agencies could access this technology for tracking terrorists or other suspicious individuals. 

Internet marketing companies could track the number and make-up of viewers watching an ad, according to the research presented at the Black Hat Europe meeting in London.

"It's important to know that video encryption is not as secure as we once thought," Dubin said

"Google, YouTube's parent company, is not likely to patch the gaps, since it would be prohibitively expensive to create a traffic obfuscation mechanism for every user's every video request," he added.