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Written by Jakub Rusinowski · Last updated September 1, 2026
Founder, LLM Configurator — AI educator & workshop leader on local LLM deployment
Windows protected your PC
Microsoft Defender SmartScreen prevented an unrecognized app from starting. Running this app might put your PC at risk.
This app has been blocked for your protection.| If you see | The cause is | Go to |
|---|---|---|
| "Windows protected your PC" on a downloaded installer | SmartScreen does not recognise the publisher — most open-source AI tools are unsigned | Fix 2: verify it, then More info → Run anyway |
| A multi-gigabyte .gguf disappears from Downloads mid-write | Real-time protection quarantined it during the scan | Fix 3: add a folder exclusion for the model store only |
| Model downloads crawl and the disk is busy but the network is not | Defender is scanning every block as it is written | Fix 3 — same fix, different symptom |
| "This app has been blocked for your protection" | A policy block, not SmartScreen — often a work-managed device | Fix 5: this is your IT department, not a setting |
| The file downloaded but the app will not launch it | The Mark-of-the-Web attribute is still on the file | Fix 2: Properties → Unblock |
Two different security systems are involved and conflating them is why people fail to fix this. One stops installers from running. The other silently eats model files. They have different causes, different fixes, and very different risk profiles.
SmartScreen gates unrecognised *applications* by reputation. It is not scanning for malware: it is asking whether this exact binary, signed by this publisher, has been seen enough times to be trusted. Most local-AI tooling is small open-source projects without an expensive code-signing certificate, and a fresh release of even a well-known project starts with no reputation at all — so it trips the warning legitimately, and will keep tripping it after every release. Real-time protection is a separate system that scans every file as it is written. A 20–40 GB model file being streamed to disk means sustained scanning of a very large opaque binary, which both slows the download considerably and occasionally results in the file being quarantined. Same vendor, same Security app, entirely different mechanisms — and a fix for one does nothing for the other.
Do this first, every time. Download only from the project's official domain — not a search result, not a mirror, not a link in a forum reply. Compare the SHA-256 against the checksum the project publishes, where it publishes one. Check the digital signature in the file's properties: some projects are signed even when SmartScreen has not yet accrued reputation for them, and a valid signature from the expected publisher is strong evidence. If any of these fails, stop — do not proceed to the rest of this page.
⚠️ Every remaining fix on this page weakens a protection that exists for good reason. They are safe for a binary you have verified and reckless for one you have not. If you cannot verify the file, the correct action is to not run it.
# PowerShell — hash it and compare against the published value
Get-FileHash .\OllamaSetup.exe -Algorithm SHA256
# Is it signed, and by whom?
Get-AuthenticodeSignature .\OllamaSetup.exe |
Select-Object Status, SignerCertificateValid with a signer you recognise (or the project is openly unsigned and you obtained it from its own domain).For a single verified installer there are two narrow options and you should use one of them rather than anything broader. In the SmartScreen dialog, click More info → Run anyway, which affects that one launch. Or right-click the file → Properties → tick Unblock → OK, which removes the Mark-of-the-Web from that single file and nothing else. Unblock-File is the PowerShell equivalent. Neither changes any setting; both are scoped to one file.
# PowerShell — remove Mark-of-the-Web from ONE verified file
Unblock-File .\OllamaSetup.exe
# Confirm the zone marker is gone
Get-Item .\OllamaSetup.exe -Stream * | Select-Object StreamZone.Identifier, and the installer launches without the SmartScreen dialog.Get-Item .\OllamaSetup.exe -Stream Zone.Identifier -ErrorAction SilentlyContinueFor the vanishing-and-slow-download problem, add a Defender folder exclusion for your model store: Settings → Privacy & security → Windows Security → Virus & threat protection → Manage settings → Exclusions → Add an exclusion → Folder. Point it at the models directory and nothing else. Not the whole drive. Not your user profile. Not C:\. The store is a well-defined location holding large opaque blobs that scanning cannot meaningfully assess, which is exactly the case exclusions exist for — and it stays that way only if the exclusion stays narrow.
⚠️ An exclusion means Defender stops inspecting anything written into that path, including anything a compromised tool writes there later. Keep it to the model directory, and remove it if you stop using that directory.
# PowerShell as Administrator — the model store only
Add-MpPreference -ExclusionPath "$env:USERPROFILE\.ollama\models"
# Review what is excluded, and remove one when you are done with it
(Get-MpPreference).ExclusionPath
Remove-MpPreference -ExclusionPath "$env:USERPROFILE\.ollama\models"ollama pull gemma3:1b
ollama listIf a download vanished, it may be in quarantine rather than deleted. Windows Security → Virus & threat protection → Protection history lists recent actions and offers restore. Restore it only if the detection was on a model file you obtained from a source you have verified — a genuine detection on an executable is not something to override. Add the folder exclusion afterwards so the same download does not disappear again.
# PowerShell as Administrator — what has been detected recently?
Get-MpThreatDetection | Select-Object -Last 5 ActionSuccess, InitialDetectionTime, ResourcesThis is the advice you will find on other sites and we do not recommend it. Turning off SmartScreen or real-time protection system-wide to install one program trades a five-second dialog for permanently reduced protection on the whole machine — and people never turn it back on. Everything above achieves the same outcome with a blast radius of one file or one folder. If a block message names your organisation rather than SmartScreen, it is a managed-device policy: your IT department can allow the application, and working around a policy block on a work machine is not a technical problem.
Some of this is self-inflicted. Each 20–40 GB file is a large, slow, opaque write that antivirus must chew through, and most of those files turn out to be models too big for the machine's VRAM anyway. Pulling a model matched to your hardware means smaller downloads, faster scans, less quarantine surface, and fewer exclusions to maintain.
If the installer now runs and the terminal still cannot find the command, that is a PATH problem rather than a security one. If model files keep filling the drive after this, moving the store is the next step — and remember an exclusion follows the path, so a moved store needs its exclusion moved too.
Include this when you report it
Get-AuthenticodeSignature on the fileGet-MpThreatDetection | Select-Object -Last 5SmartScreen judges reputation, not content. An installer that is unsigned, or signed by a publisher it has not seen often, gets the warning regardless of whether the software is safe. New releases of well-known projects trip it routinely until enough people have run them.
Only after you have verified the file: downloaded from the project's own domain, hash matching the published checksum, and a signature you recognise where one exists. With those checks done it is reasonable. Without them you are running an unverified binary with full user rights.
Most likely into Defender quarantine during the write. Check Windows Security → Virus & threat protection → Protection history, restore it if the source is one you trust, and add a folder exclusion for the model directory so the next download is not scanned block by block.
No. Exclude the model directory specifically. A drive-wide or profile-wide exclusion stops Defender inspecting everything written anywhere under it, which is a far larger hole than the problem you are solving and one you will forget you opened.
Not with a setting, and you should not try. That is a managed-device policy rather than SmartScreen, and it is enforced above your account. Ask IT to allow the specific application — most will for a mainstream tool with a business case.