Microsoft has quietly but decisively removed Microsoft Defender SmartScreen from Internet Explorer and IE Mode on Windows 11, a change documented in a freshly published support bulletin that reframes how legacy browsing scenarios are protected inside modern Windows releases. The deprecation means that while SmartScreen still defends users in Microsoft Edge, the Windows Shell, and other supported pathways, the SmartScreen checks that used to run inside IE or when pages are rendered in IE Mode no longer execute on Windows 11 — a move Microsoft says is part of a broader modernization effort to retire legacy components and consolidate protections in modern, supported surfaces.
Background / Overview
Microsoft Defender SmartScreen is a reputation-based security service built to reduce phishing and malware exposure by checking URLs and downloads against cloud-managed threat intelligence and local heuristics. It performs three primary roles:- Website protection — comparing visited URLs to lists of reported phishing and malicious domains and surfacing interstitial warnings.
- Application/file reputation — evaluating downloaded executable files and installers for known-bad or unknown (low-prevalence) status.
- Integration with Mark‑of‑the‑Web (MoTW) — honoring file provenance metadata so that files originating from the Internet trigger platform protections when later opened.
Why Microsoft removed SmartScreen from IE and IE Mode
Microsoft’s bulletin and related documentation list several interlocking reasons for the deprecation. The decision is not a single-issue removal; it stems from architecture, policy, and operational risk trade-offs.1. IE and IE Mode’s intended use is narrow and enterprise-focused
IE Mode is explicitly designed for enterprise customers to run trusted, internally managed legacy web apps that require older document modes or ActiveX behaviors. It is not intended for general Internet browsing. Because IE Mode is meant to host a controlled list of trusted intranet or line‑of‑business endpoints, Microsoft concluded SmartScreen’s URL-based anti‑phishing work was redundant in those scenarios when the site list is properly scoped.2. Legacy SmartScreen components were dependent on deprecated binaries
The SmartScreen codepaths used by Internet Explorer relied on legacy binary components and libraries that Microsoft removed as part of a broader platform modernization effort. Keeping those legacy components alive to support SmartScreen inside IE would reintroduce the very attack surface Microsoft aims to shrink and would risk unpredictable behavior across updated Windows builds. Microsoft says removing these binaries made retaining SmartScreen in IE impractical and unstable.3. Consolidation of protection into modern surfaces
Microsoft’s security model now concentrates capabilities in Edge and platform services (Windows Shell, Defender, and Microsoft Defender for Endpoint). Those services continue to run SmartScreen checks for downloads and provide URL reputation protections where the platform is designed to support them reliably. Files downloaded via IE/IE Mode still receive a Mark‑of‑the‑Web flag and are evaluated later by SmartScreen in the Windows Shell when executed — so Microsoft places the safety net at the platform boundary rather than inside an outdated browser runtime.What this actually means for users and administrators
Short answer: external browsing should be done with Microsoft Edge; IE Mode should be restricted to trusted legacy apps; and platform protections still operate for files via MoTW and Windows Shell SmartScreen.Practical effects
- Opening Internet Explorer directly on Windows 11 redirects to Microsoft Edge and IE Mode is the only supported way IE code will run on Windows 11. SmartScreen checks that used to execute inside the IE/IE Mode process are no longer performed in that process on Windows 11.
- Files downloaded in IE/IE Mode still get the Mark‑of‑the‑Web (MoTW) Zone.Identifier metadata. When those files are opened later (for example, from File Explorer), the Windows Shell SmartScreen and Attachment Manager will still evaluate them and may block or warn based on reputation and policy. That preserves a key defensive control for download-originated threats.
- SmartScreen continues to guard browsing and downloads in Microsoft Edge, and administrators can still centrally configure SmartScreen behavior via Group Policy and Intune MDM settings.
Recommended configuration changes (high level)
- Ensure IE Mode site lists are tightly scoped to known, internal applications only. Treat IE Mode as a compatibility bridge, not a general-purpose browser.
- Encourage or enforce the use of Microsoft Edge for all Internet‑facing browsing and downloads.
- Validate that Windows Security > App & browser control > Check apps and files (the Windows Shell SmartScreen setting) is enabled for endpoints that require an extra safety net. Administrators can lock SmartScreen behavior via Group Policy or MDM.
Security analysis — strengths, but real trade-offs remain
This change has defensible engineering logic: removing outdated runtime dependencies reduces attack surface, simplifies maintenance, and channels protection into actively developed services. However, the move also introduces important operational and threat-model considerations.Strengths of the decision
- Reduced legacy attack surface: Legacy SmartScreen binaries in IE would have required ongoing compatibility support and security maintenance. Removing them removes a source of complexity and potential regressions.
- Centralized, modern protections: SmartScreen in Edge and Windows Shell is actively maintained, benefits from cloud telemetry, ML enhancements (for example, the Edge scareware‑blocking features), and is easier for Microsoft to update rapidly.
- Policy clarity for enterprises: The advisory reinforces the boundary between legacy compatibility (IE Mode) and mainstream browsing (Edge), nudging organizations toward migrating legacy apps or isolating them behind strong controls.
Risks and gaps to watch
- Assumptions about trusted site lists: IE Mode’s security model depends heavily on correct site-list configuration. If organizations misconfigure site lists (for convenience or expedience), they may inadvertently allow external, untrusted content to run in a less-protected IE runtime. Bad trust mappings are an obvious vector for social‑engineering or zone‑mapping abuse.
- MoTW limitations and bypass techniques: Relying on Mark‑of‑the‑Web plus later Windows Shell checks is sensible — but MoTW is not infallible. Several techniques and vulnerabilities exist that strip, fail to propagate, or otherwise bypass MoTW (for example, malicious archive extraction, non‑NTFS transfers, or certain extraction bugs). Attackers can exploit these behaviors to deliver payloads that avoid SmartScreen warnings until after execution. Administrators should treat MoTW as one layer among many, not the single ground truth.
- User behavior and training: If users are unaware that IE Mode lacks in-context SmartScreen protections on Windows 11, they may assume the same interstitials and download blocks will appear and proceed unsafely. Clear communication and policy enforcement are necessary.
Concrete, prioritized actions for administrators
- Audit IE Mode usage and site lists
- Inventory all entries in your IE Mode site lists and confirm each entry maps to a legitimate, internal web app or intranet resource.
- Remove any wildcard entries or broad domain inclusions (for example, *.example.com) unless strictly necessary; prefer precise, single-host entries to minimize accidental trust escalation.
- Enforce modern browsing for Internet‑facing content
- Direct users to Microsoft Edge for public web browsing and downloads.
- Use device configuration policies (e.g., Microsoft Endpoint Manager / Group Policy) to make Edge the default browser for managed devices where feasible.
- Ensure Windows Shell protections are configured and monitored
- Verify Windows Security > App & browser control > Check apps and files is enabled where appropriate, and consider locking the setting centrally so users cannot disable it.
- Enable Defender for Endpoint and EDR telemetry to correlate suspicious download activity with endpoint behavior for rapid detection.
- Harden zone mappings and related registry/policy entries
- Audit ZoneMap registry keys and Group Policy settings that control Trusted Sites and Intranet zone behaviors. Remove or tighten entries that may grant implicit trust to external content.
- Avoid broad network share trust assignments that would strip files of MoTW protections or cause them to be treated as intranet-originated.
- Test and validate extraction/processing workflows
- Confirm that common business workflows (archival tools, document pipelines, automated unpacking services) preserve MoTW where appropriate, or that alternative controls exist (antivirus scanning, sandboxing) when MoTW cannot be relied on.
- Where compressed archives or disk images are in use, ensure extracted files are scanned by EDR/AV solutions and that extraction software is up to date to avoid known MoTW extraction bugs.
- Communicate and train
- Update user-facing guidance to clarify that IE/IE Mode on Windows 11 no longer runs SmartScreen checks in-process and that Microsoft Edge and Windows Shell provide the platform protections.
- Train support staff and helpdesk teams to handle tickets where users expect Edge‑style interstitials while using IE Mode.
Verifiability and independent cross‑checks
Key claims in the advisory are verifiable against Microsoft documentation and independent reporting:- Microsoft’s platform documentation explains how SmartScreen operates in Edge and via Windows settings and policies (policy names and the “Check apps and files” control).
- Industry coverage and feature reporting (for example, Edge’s scareware blocker and recent SmartScreen enhancements) underscore Microsoft’s ongoing investment in modern surface protections even as legacy pieces are retired.
- The Mark‑of‑the‑Web behavior and its role in later platform checks are documented and discussed in multiple security advisories and community write‑ups; those sources also highlight known bypass techniques that administrators must mitigate.
Final assessment — a pragmatic security trade
The removal of SmartScreen from Internet Explorer and IE Mode on Windows 11 is a pragmatic, security-minded move: it eliminates fragile legacy dependencies and channels protection into actively supported surfaces where Microsoft can iterate quickly. For most modern deployments this is a positive consolidation.That said, the change places more responsibility squarely on administrators to get IE Mode trust boundaries right and to ensure platform protections like Windows Shell SmartScreen, Defender for Endpoint, and file-handling hygiene (MoTW handling, compression/extraction behavior) are robustly configured. Where organizations rely on older toolchains or extraction workflows that strip MoTW, compensating controls (strong EDR, sandboxing, file integrity checks) must be in place.
For enterprise teams, the immediate checklist is straightforward: tighten IE Mode site lists, enforce Edge for external browsing, verify Windows Shell SmartScreen and Defender policies, and test any file-handling pipelines that could erode MoTW provenance. Those steps will preserve defence-in-depth and mitigate the primary risks introduced by moving SmartScreen out of the legacy IE runtime.
In sum, this is a change that aligns engineering intent with security policy: shrink legacy code, strengthen modern endpoints, and force the hard decisions about where real trust belongs in an enterprise environment. The technical benefits are clear, but successful outcomes will depend on disciplined policy management, validation of file-provenance controls, and proactive migration away from legacy IE dependencies.
Source: Microsoft Support SmartScreen deprecation in Internet Explorer and IE Mode in Windows 11 - Microsoft Support
