Notepad++ updater compromise: what happened and what users should do

Notepad++—a widely used Windows text editor—warned that its update infrastructure was compromised for months, enabling attackers to selectively redirect some users to malicious updates. Ars Technica reports the compromise began in June 2025 and that control wasn’t fully restored until December.

This is a classic supply-chain pattern: instead of exploiting each victim directly, attackers target the update path so the software itself becomes the delivery vehicle.

What the attack looked like

According to Ars, the attackers gained “infrastructure-level” control that let them intercept and redirect update traffic destined for the Notepad++ domain. Instead of every user being hit, the redirection was selective—aimed at targets of interest.

That selectivity is an important clue. It suggests the attackers either had a specific victim set or were trying to avoid detection by keeping infection volume low.

Why updaters are such a high-value target

Auto-update mechanisms are designed to do three dangerous things:

Fetch code from the internet
Write it to disk
Execute it

That’s exactly what malware wants. The only thing standing between “update” and “infection” is verification.

If an updater:

Doesn’t use strong TLS consistently
Doesn’t verify signatures correctly
Trusts a tamperable manifest file

…then intercepting or redirecting traffic can be enough to swap the payload.

The Notepad++ updater specifics (and the weak points)

Ars describes a bespoke updater (GUP / WinGUP) that:

Reports its version to a Notepad++ URL
Retrieves update instructions from an XML file
Downloads an installer to a temp directory and runs it

The weak point in many systems is the “manifest” step. If the manifest can be replaced or altered, the updater can be pointed at any download location.

What versions users should be on

The Ars report notes developers urged users to ensure they are running version 8.9.1 or higher.

As a rule of thumb in incidents like this:

Prefer manual installation from the official site
Avoid third-party “download mirrors” and ad-filled search results
Treat unexpectedly timed update prompts as suspicious

How to assess your exposure

There may not be perfect indicators of compromise for a targeted campaign, but you can reduce uncertainty:

Confirm your installed version and compare it to current releases.
Verify the installer signature for the Notepad++ binaries you have.
Review system logs for unusual process launches around update times (installer processes you don’t recognize, network calls to unusual domains).
Scan with EDR/AV that can detect known backdoors reported by incident responders.

For organizations, it’s also reasonable to:

Restrict updater components from reaching the internet
Use controlled software deployment (MSI packaging, internal repositories)

What this says about open-source dependencies

Notepad++ is free, heavily used, and often underfunded relative to its importance. That mismatch shows up as brittle infrastructure and custom update systems that weren’t designed for nation-state-level threat models.

The broader lesson is not “don’t use open source.” It’s that widely depended-on open-source projects need:

Modern update frameworks
Security reviews
Funding for infrastructure and incident response

Bottom line

If you use Notepad++, assume the update channel was a potential attack surface in 2025. Get to a current version, prefer official/manual installs, and treat updater integrity (signatures and manifests) as the real security boundary.