The behavioural analytics firm reports a doubling in the deletion rates for Flash cookies – technically known as local shared objects (LSOs).

Nine months ago, Scout said, just 3% of LSOs were deleted from the more than 600,000 devices the company tracks. Now that figure is up to 7%.

The issue with deletion is that it leads to duplicate cookies being created on an individual device, causing counts of unique browsers to be inflated.

Widespread deletion of standard HTTP cookies has severely harmed their reliability when used as a form of user measurement – Scout’s own research says HTTP cookie counts overstate a website’s audience upwards of two to four times.

This situation led increasing numbers of web content providers to turn to Flash cookies for web tracking purposes, as they had the advantage of being less well-known by consumers, less easy to delete and were unaffected by private-browsing modes within web browsers.

But those advantages swiftly became disadvantages when a group of Berkeley university researchers published a paper exposing the growing use of LSOs and some unethical practices such as cookie respawning, whereby Flash cookies are used to recreate deleted HTTP cookies, clearly against web users’ wishes.

Flash developer Adobe weighed in on the issue too, condemning companies for overriding consumer privacy preferences and pledging to make it easier for users to find and manage their cookie settings in the newest version of its Flash Player software, which is due to be released this summer. Private browsing modes will also be supported.

All of which gives Flash cookies a limited shelf life, says Scout Analytics’ Matthew Shanahan: “Publishers and ad networks alike have increased their use of Flash cookies exponentially, which for now provides an advantage over HTTP cookies. The question is, for how long?

He adds: “Our findings indicate an early, but growing awareness of Flash cookies and how to manage them, making it only a matter of time before their error rate cannot be overlooked.”