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Privacy Policy

For the purposes of this policy we define you to be a member if you have signed in to an account. Until you have signed in you remain a visitor.

What cookies does the website use?

By default your connection to the website will use a secure SSL connection (HTTPS). If you choose to use a non-secure connection (HTTP) then it is necessary for a cookie (name = non_secure) to be stored on your computer to override the default setting. If you have disabled cookies then you will not be able to switch to a non-secure connection.

This website makes use of MathJax: a JavaScript engine that displays mathematical notation in web browsers. When you view any problem page, or if a member views a problem thread, the MathJax website will place a cookie (domain =, name = __cfduid) on your computer.

Project Euler uses PHP sessions which means that a cookie (name = PHPSESSID) will be stored on your computer. The PHP session is primarily used for members and so it is necessary for cookies to be enabled to be able to sign in. The PHPSESSID cookie will be automatically removed when you close your browser.

As a visitor no other cookies will be used.

What cookies do you store for members?

As mentioned above, Project Euler makes use of PHP sessions and the PHPSESSID cookie is used as your unique identifier which keeps members signed in. As long as you remain active on the website your session will remain alive, but after a period of inactivity the session will expire and a new cookie will be generated, requiring you to sign in again. However, it is possible, when signing in, to click "Remember Me". If this box is checked then an additional cookie (name = keep_alive) will be stored on your computer allowing you to be automatically re-authenticated when your session expires. This cookie will remain on your computer until it expires or until you sign out. See About persistent logins... for more information.

As a member you also have the option of sorting the problems table by: problem ID or solved by, and to filter the problems by: all, solved, or unsolved. By default it will sort by ID in ascending order and all problems will be shown. If you change any of these settings then one or more cookies (name = sort_type; name = sort_method; name = filter_type) will be used to remember your selections.

Similarly, if you decide to only show active members in the statistics tables, then an additional cookie (name = statistics_show) is used to enable this view from table to table. If you restore the view to all members, then the cookie is deleted.

When you sign out all cookies related to the Project Euler website will be removed. However the PHPSESSID cookie will remain until you close your browser.

What personal information do you keep in the database?

The primary purpose of creating an account is to keep track of which problems you have solved, and as you continue to solve the problems you will earn awards. Accounts are anonymous (we do not store email addresses, IP addresses, or any other data which might be used to identify an individual) and they are accessed by your username and password; passwords are stored using the latest PHP native one-way hashing algorithms. We do not require any personal information. However, on your account page you may choose to select your country, preferred programming language, and enter any additional information about yourself which you wish to be made public. You can also add friends to your profile, set your time zone, and select a colour/style theme.

Who can see my information?

By default your username will appear in the public ranked tables. Through these tables other members will be able to see how many problems you have solved, which awards you have earned, any additional information which you entered about yourself on the account page, and your country/preferred programming language if you chose to set them.

The detailed information found on your progress page is private, but any friends you have added will be able to see your progress page.

Can I hide my information from the public ranked tables?

Yes. On your account page you will find a maintenance section at the bottom. In this section you can choose to make your account private. This will remove your username from all public ranked tables, including the fastest solvers, and you will not be included in any of the statistics. Be aware that making your account private is permanent and you cannot revert to public after this change has been made.

However, please note that the posts made in the problem threads are public. If you make a post then your username will appear next to your post. If you have set your country/preferred programming language then these will also appear. Making your profile private will not hide this information from public posts.