Flash-based websites will invariably plant flash cookies (also called Locally Shared Objects or LSOs) on your computer. A flash cookie is able to handle more complex information than a browser cookie and is able to pass information across the different browser types you may have installed on your computer.
There are many bona fide uses of flash cookies. Banks, for example, might use a flash cookie to recognise your computer and thus add a extra level of security to your account.
However, the use of flash cookies can also be abused and be invasive of your privacy and surfing habits.
How to avoid flash cookies
Editor's note: Since the end of Flash Player, the following guide might be out of date. If you need help managing your cookies, please refer to our guide on how to clear cookies.
Previously, when you visited a Flash-enabled site, you'd get a notification asking your permission to download Flash elements. Now that Adobe prevents its Flash Player from running Flash content, you may not see this notification and might see an error message instead.
To delete existing flash cookies, click the tab on the right side labeled "Website Storage Settings". You'll see a list of websites. Click Delete Website or Delete All Sites to clear flash cookies.