Researchers have found that new technologies such as HTML5 are being used by sites to store cookies and track visitors' web use.
HTML5 is a language used for presenting web content, which makes it easier for sites to show multimedia and visual content.
In a paper entitled Flash Cookies and Privacy II: Now With HTML5 and ETag Respawning, the researchers surveyed 100 web sites and examined how they store cookies on users' machines.
They found that many sites placed over 100 different cookies, and that many of these were installed by third parties and not the sites actually visited.
Seventeen of the sites surveyed stored HTML5 cookies, which could enable the tracking of web users' online behaviour.
"HTML5 storage offers many advantages over ordinary cookies, and may become a more universal tracking mechanism. Like Flash cookies, HTML5 storage is more persistent than HTTP cookies."
The researchers added that HTTP cookies expire by default, whereas HTML5 data is persistent until deleted by a web site or user.
They found that Twitter, the New York Times and Hulu were among the web sites to store HTML5 cookies on users' machines.
Yesterday, the European Network and Information Security Agency (ENISA) proposed a list of fixes to HTML5, among other technologies, in order to improve cyber security.
In June this year, in a speech on online privacy, vice president of the EU Neelie Kroes highlighted concerns that cookies are being used to track users without their knowledge.
She stated that users should have the right to control that information.
"Users should be able to know, and control, when and to whom they give their information and how it will be used," said Kroes.