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A tracking pixel can tell an email or document sender that software requested a remote image and may expose request metadata. In the 2017 CyberScoop report, Check Point described attackers using those signals to identify responsive recipients and shape later phishing attempts. The pixel is a reconnaissance beacon—not, by itself, proof that the device was infected or compromised.
What a tracking pixel reveals
A tracking pixel is usually a tiny, remotely hosted image embedded in an email or document. Instead of storing the image inside the message, the sender inserts a URL to a server they control. When the recipient’s mail client or document viewer requests that URL, the server can log the request.
Depending on the client, privacy controls, network path and server configuration, a request may include an IP address, host name, operating system, browser or application type, viewing time, cookies or other request information. Those fields are conditional; every pixel request does not expose all of them.
Network Advertising Initiative, quoted by CyberScoop, noted that “Often the image is designed to blend into the background.” That makes the beacon difficult to notice without examining message source or network activity.
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How attackers turn a pixel into phishing intelligence
1. Confirm that a message reached a usable account
A request can indicate that a message was opened or that a document viewer loaded its remote content. Attackers can compare which messages generate requests and which do not, helping them distinguish active or valuable addresses from inactive ones.
2. Group recipients by environment
Request metadata can provide clues about software, networks and timing. An attacker might use those clues to separate corporate accounts from personal accounts, identify likely high-value targets or tailor lures to the recipient’s apparent environment. These are capabilities described in the reporting, not guaranteed results of every request.
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3. Prioritize follow-up attacks
Once a sender knows who responds and when, later phishing can be aimed at the most promising recipients. Donald Meyer of Check Point told CyberScoop in 2017, “You can build a ton of ‘get’ requests into the image,” describing the pixel as a probing and information-gathering tool.
The report’s central point is reconnaissance: collecting signals before a subsequent attack. It does not demonstrate that the image itself executed malware or compromised a recipient’s device.
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Pixels in Office and cloud documents
CyberScoop and a related Check Point article also described remote images in Office documents and cloud-hosted files. If a viewer loads the linked image, the file’s server can receive a request. Forwarding the document can create additional opportunities for requests when new recipients open it.
Those articles date from 2017 and do not establish default behavior for every current Office edition, viewer or security configuration. Whether a request occurs depends on the application, document settings, network controls and privacy features in use.
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What this technique does—and does not—prove
- It can provide a beacon: a remote server may learn that software requested an image and record available request data.
- It can support targeting: attackers may use response patterns and environmental clues to select or customize later phishing.
- It is not automatically an infection: the cited 2016–2017 reporting describes information gathering, not executable code delivered by the pixel itself.
- It is not a guaranteed identity or location record: proxies, relays, blocked images, shared networks, unique URLs and server settings can change what is observable.
How current mail clients reduce pixel exposure
Blocking and privacy relays address remote images differently. Use the instructions for the platform you actually use; classic Outlook steps do not apply to Outlook mobile.
| Client or feature | How it handles remote images | What that changes |
|---|---|---|
| Classic Outlook for Microsoft 365 and Outlook 2016, 2019, 2021 and 2024 | Microsoft says automatic internet picture downloads are blocked by default in the listed classic versions. Users can download pictures selectively for a trusted message. | Blocking can prevent some automatic pixel requests until the user permits images. |
| Outlook mobile | Microsoft documents a separate “Block external images” setting. | Mobile configuration must be checked independently; classic Outlook menu paths should not be assumed. |
| Apple Mail Privacy Protection | Apple says remote content is fetched in the background by default through two relays operated by different entities. | Apple says the sender cannot use the recipient’s IP as a unique identifier to connect activity across websites or apps. This mediates the request rather than simply blocking every image. |
Neither approach, as described by the vendors, establishes that link tracking, attachment telemetry or every other form of measurement is blocked. A protected image request can still differ from no request at all.
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Practical steps for individuals
- Keep automatic external-image loading disabled unless you have a reason to trust the message and sender.
- When a message is expected, use the client’s per-message option to download pictures rather than enabling them globally.
- Check whether your mail app offers a privacy relay or external-image blocking feature, and review its current setting after app or account changes.
- Treat an unexpected message that appears to know your activity, employer or software as a phishing warning—not as proof that your device has been hacked.
- Use your organization’s reporting button or security team for suspicious messages instead of replying or opening linked attachments.
What organizations should review
- Whether managed mail clients block or mediate external images by default.
- How mobile mail policies differ from desktop policies.
- Awareness training that explains why an image fetch can be reconnaissance without claiming that every pixel is malware.
- Reporting and triage procedures for messages that may have collected engagement or environment data.
- Document-sharing and Office viewer configurations, especially for files received from untrusted sources.
How current is the evidence?
Shaun Waterman’s CyberScoop report was published April 17, 2017, drawing on Check Point commentary and a September 8, 2016 Check Point article. Those sources establish that the technique was being reported and used as a reconnaissance concept at that time. They do not provide a current prevalence rate, a global estimate or evidence that the same behavior is universal across 2026 mail clients and Office versions.
Donald Meyer summarized the 2017 rationale as follows: “Hackers are always looking for the low-hanging fruit.” That remains a useful explanation of the tactic’s purpose, but it should not be read as a measurement of how common malicious pixel reconnaissance is today.
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