Cookies, P3P, and IE6

How Internet Explorer 6 Handles Cookies and Privacy

By the time IE6 was released, most desktop browsers on the market were still using a relatively simple cookie model. The idea was straightforward: a website could set a small text file on the visitor’s computer, and that file would be sent back to the same site on each subsequent request. The file held data such as a session identifier, a shopping‑cart snapshot, or a preference flag. The browser, by default, accepted these files without asking the user. This made it easy for site owners to personalize experiences and for marketers to track behaviour across multiple sites.

However, the growing concern over privacy and data misuse led Microsoft to rethink how cookies should be handled. In IE6, they introduced a built‑in privacy policy framework called P3P (Platform for Privacy Preferences). The goal was to give users a way to set a single privacy level that would automatically apply to all sites, instead of having to negotiate each cookie individually. Under this model, the browser would read a machine‑readable summary of a site’s privacy practices from a file called p3p.xml. If the summary matched the user’s selected privacy level, the browser would accept the cookies; otherwise it would reject them or ask for consent.

IE6 grouped sites into three zones: Local intranet, Trusted sites, and Internet. For each zone a user could set a privacy level from “Accept All” to “Reject All.” Most Windows users left the default setting at “Medium,” which means the browser would accept cookies only if the site’s p3p.xml declared that it respected certain privacy norms. Because this default is so common, a large percentage of web traffic today is filtered through this mechanism. If a site does not supply a valid P3P declaration, any cookies it sets are treated as non‑compliant and are therefore blocked or hidden from the user’s cookie store.

This change had a ripple effect on the industry. Site owners had to rethink how they handled user data. They could no longer rely on simple cookie acceptance; they needed to provide a clear statement of what they collected, how they used it, and how they protected it. The statement had to be encoded in XML so that IE6 could read it automatically. If the site failed to do this, visitors using the default IE6 settings would see a small warning icon in the status bar, indicating that a cookie was being blocked. The icon could be clicked to view the list of cookies, but the user would not be able to interact with them in any way, such as deleting or editing the value.

For web developers, this meant a new layer of compliance. They had to learn the syntax of the P3P header and embed it in each HTTP response. They had to decide which privacy principles to claim - many used the “Basic” or “Extended” categories defined by the W3C. The P3P header is also useful for affiliate marketing. When a visitor clicks a link that passes a tracking cookie to an affiliate site, the affiliate must also publish a P3P policy. If the affiliate’s policy is missing or incomplete, the cookie is blocked, and the original site never receives credit for the referral. In effect, the entire commission chain can collapse because of a single missing XML file.

In short, the introduction of P3P in IE6 made it essential for any site that relies on cookies to publish a privacy policy that can be automatically read by the browser. It was not enough to write a privacy statement on a landing page; it had to be structured, machine‑readable, and correctly referenced in the p3p.xml file. Failure to do so risks alienating a large segment of the user base, especially those who value privacy and who rely on the browser’s default settings to protect it. The next sections will walk through how to craft that policy, host the required files, and verify that everything works as intended.

Creating and Deploying a P3P Privacy Policy

The first step toward P3P compliance is to produce a policy that describes exactly what information you collect, how you store it, and for how long. This policy is expressed as a JSON‑like structure in XML, and is typically stored at /w3c/p3p.xml relative to your website’s root directory. The browser uses this file to determine whether to accept cookies from your domain. Below are the key elements you need to include and how to generate them.

1. Define the policy string. The policy string is a compact representation of the privacy practices. It consists of one or more “p” elements, each containing three fields: an action, a content, and a privacy principle. For example, <p action='b' content='<' cp='id'/> declares that the site will not use the user’s identity (id) for the purposes specified by the action b (for “before”). Common actions include c (client side), e (server side), f (first‑party), and t (third‑party). The content field indicates the scope, such as <gt; for all data, or cookie for only cookies. The cp field lists the privacy principle code, like id, p, t, c, etc. A full list of accepted codes is available at the W3C P3P page.

2. Embed a reference to the privacy policy page. The p3p.xml file must include a <link> element that points to a publicly accessible page containing the full human‑readable policy. For example: <link href='https://www.example.com/privacy.html' rel='P3P' type='text/html'/>. This link allows visitors to read the full policy if they wish to understand the data practices beyond the terse XML summary.

3. Test the XML for well‑formedness. The file must be valid XML. A simple validation can be done with any XML editor or online validator. Common errors include missing closing tags or incorrect quoting. Even a small syntax error will cause IE6 to reject the policy entirely.

Once the p3p.xml file is ready, you must place it in a directory named w3c at the root of your site. The full path is typically https://www.example.com/w3c/p3p.xml. The file must be publicly accessible; if the server returns a 403 or 404 status, the browser will not find it. After the file is live, add the P3P header to every HTTP response that sets a cookie. The header looks like this: P3P: CP="IDC DSP COR ADM DEVi TAIi PSA PSD IVAi IVDi CONi HIS OUR IND CNT". The CP attribute holds the policy string, and the string should match the one defined in p3p.xml. If you use a server‑side framework, many libraries provide helpers to add this header automatically.

One common pitfall is to only add the P3P header on pages that use cookies, while forgetting to do so on static assets like images or JavaScript files that also rely on third‑party cookies. Since the header is evaluated per request, any resource that sets a cookie and fails to include the header will be blocked under medium or high privacy settings. Therefore, it’s a good practice to include the header on all responses, or at least on all endpoints that set cookies.

For sites that depend on third‑party services - such as ad networks, analytics providers, or affiliate links - it is often insufficient to declare your own policy. You must also ensure that each third‑party domain publishes a compliant P3P file. If they do not, any cookies they set will be blocked, and you may lose valuable data or commission. If you have control over the third‑party code, reach out to the provider to request that they add a P3P policy. If not, consider using a different provider that already complies.

After deployment, you should monitor the cookie acceptance rates of your site. Tools such as Google Analytics report cookie usage per browser; if you see a spike in blocked cookies for IE6, it likely indicates a P3P issue. Fixing these problems early ensures a smoother user experience and protects your revenue streams from affiliate programs.

Testing and Verifying Your P3P Implementation in IE6

Deploying a P3P policy is only half the battle. Without proper testing, you may still run into situations where cookies are blocked. The following checklist walks through the steps you can take to confirm that IE6 correctly reads and respects your policy.

1. Open IE6 and navigate to Tools > Internet Options. Under the Privacy tab, set the privacy level to Block all cookies. This forces the browser to block any cookie that does not match a compliant policy. Now browse to a page on your site that sets a cookie. On the status bar, you should see a small icon - a red warning sign with an eye icon. Clicking it will display a list of cookies that were blocked. Verify that the cookie you expect to be set appears in the list, confirming that IE6 recognized your attempt to set a cookie but blocked it due to lack of a matching P3P declaration.

2. Return to the Privacy tab and change the setting to Medium, which is the default for most users. Refresh the page. If your P3P file and header are correct, the warning icon should disappear, indicating that the cookie is now being accepted. Double‑click the icon again; it should now show a smaller list or no warning, depending on the policy’s string. This confirms that the browser is reading your p3p.xml file, matching the policy string, and allowing the cookie.

3. Use the Network Monitor or a similar tool to capture the HTTP headers of the response. Search for the P3P header. Verify that the CP attribute contains the exact policy string you defined. Any discrepancy - extra spaces, missing quotes, or a different policy ID - will cause a mismatch and result in blocked cookies.

4. Test a third‑party cookie scenario. Navigate to a site that embeds an external banner ad from a network that uses third‑party cookies, such as affiliateguerrilla.com. With the privacy level set to Medium, observe the warning icon. If the icon remains present, click it to see which cookies are being blocked. Often, third‑party sites do not publish a compliant P3P file, so their cookies will still be flagged. In that case, consider contacting the network or selecting a different partner.

5. Repeat the tests on other browsers, such as Firefox or Chrome, to confirm that your site’s cookie behavior is consistent. Some browsers ignore P3P entirely, while others still honor the policy. By ensuring that your core functionality does not depend solely on IE6, you reduce the impact of any future changes to the P3P standard.

6. Finally, maintain an audit trail. Document the policy string, the URL of the p3p.xml file, and the timestamp of the last update. Whenever you modify your privacy practices - such as adding a new analytics script - update the policy accordingly. The P3P header should always reflect the current practices; otherwise you risk having a policy that states you do one thing while your code does another.

By following these steps, you can guarantee that your site respects users’ privacy preferences in IE6 while still leveraging cookies for essential functions. This dual focus protects your users and preserves your revenue streams from affiliate and advertising partners.