Websites are placing cookies onto people’s computers that last up to 8,000 years, according to a study from a coalition of European data regulators.
The survey of European websites found that the average expiry date of a cookie was two years, but several websites – including a British one – had cookies that would only expire on December 31, 9999.
Simon Rice, group manager for technology at the Information Commissioner’s Office (ICO), said: "Setting a long expiry on a cookie means that it will not only outlive the usefulness of the device, but also the person using it at the time.
"While the length of time a cookie needs to remain on a device will depend on the reason why it was originally set, it is difficult to justify an expiry date in the year 9999 for even the most innocent of purposes."
Across Europe the average website placed 34 cookies on a person’s device during their first visit, while in the UK the number was 44.
Of the cookies surveyed 70% were third-party cookies designed by other websites, with 86% remaining on a person’s system after use instead of expiring.
"Any web developer will tell you that cookies are a vital tool for making the web work," Rice said. "However, the number of cookies out there may come as a surprise to many, particularly in the UK where the average website sets more cookies than for any of the other countries surveyed.
Regulations stipulate that users are informed by websites on their cookie use, a requirement that 94% of the British sites surveyed adhered to, well above the continental average of three-quarters.