Two US lawmakers are calling on the Federal Trade Commission to investigate so-called 'supercookies' - which aren't nearly as yummy as they sound.
Supercookies allow websites to collect detailed personal data about users, including the websites they've previously visited. Users are left unaware that such files are hidden on their web browser, and it's impossible to get rid of them, even when regular cookies have been deleted.
Researchers at Stanford University have investigated supercookies, finding Microsoft amongst the offenders - although the company says this was inadvertent, and has now put a stop to the practice.
Other companies believed to have used supercookies include Hulu, Spotify and GigaOm.
In a letter to the FTC, congressmen Joe Barton and Edward Markey say the practice raises serious privacy concerns.
"We are also very concerned about the extent of this practice by websites as well as the impact supercookies have on consumers," they say in their letter.
"Furthermore, we believe the usage of supercookies takes away consumer control over their own personal information, presents a greater opportunity for the misuse of personal information, and provides another way for consumers to be tracked online."