Ever wanted to stop a specific app from going online—whether to protect your privacy or block suspicious activity? Me too—and that’s why I use Portmaster, a free, open-source network monitor that lets you see every connection your apps make and blocks anything you don’t trust with a single toggle.
How to instantly stop any app from going online
To block an app from internet access, simply open the Portmaster app, and the left-hand sidebar will show you all running apps and services that are presently connected to the internet. Click the app you want to block—say, Google Chrome—and toggle Block Connections. It’s that simple!
Portmaster integrates directly into your system’s network stack, which allows it to see—and show you—every incoming and outgoing connection on a per-app basis. This means you can see exactly what each app is doing online and stop it if you need to.
Portmaster simply monitors, logs, and blocks incoming and outgoing connections. It doesn’t inspect every incoming and outgoing packet. For that, you’d need a packet-inspector like Wireshark—but these tools can be too technical and overcomplicated for simple home users.
Why I want to block certain apps from accessing the internet
I install a lot of different apps and tools on my PC for testing and experimentation—it comes with the job—and as you can imagine, this also exposes me to potential cyber threats. I could accidentally install something malicious that Windows Defender couldn’t detect, and now it’s quietly stealing my data in the background.
For example, I love using Obsidian to store all my personal notes because it works offline and locally stores everything. However, I also use Obsidian plugins to add extra features to the app. These are community-built, and Obsidian explicitly advises users to install them at their own risk.
While you can read the source code of these plugins to verify whether they’re malicious or not, I’m not an experienced programmer and don’t know how to audit code. So instead, I simply block Obsidian from internet access altogether. This way, even if a plugin is malicious and tries to phone home, it can’t!
When there’s a new update for Obsidian, I can temporarily disable the plugin, enable internet connectivity, and update the app. Yes, this might seem like paranoia to some, but it gives me the necessary peace of mind that my data is safe.
Do you really need a VPN on your phone?
It’s mostly all pros, but there are some cons you need to know about.
What else can you do with Portmaster
Portmaster isn’t just limited to blocking apps from accessing the internet, but functions as an overall network security tool for your Windows PC. Here’s a quick overview of its other features.
Granular view of network activity across all apps
The main dashboard shows a real-time graph of active and blocked connections, along with a list of all apps currently connected to the internet. You can dive into individual apps to see exactly which domains they’re connecting to, how much data they’re uploading and downloading, and when each connection started and ended.
Automatically block trackers and malware
One of Portmaster’s best features is automatic tracker and malware blocking. During setup, you can enable various filter lists that block known trackers, malware domains, phishing sites, and even adult content. Of course, you can also add (or remove) filters after the setup process by heading into Settings > Privacy Filters > Filter List.
Portmaster maintains a database of malicious domains and checks it in real-time, stopping these connections before they can cause issues. This happens automatically in the background—you don’t have to manually review every connection.
Per-app network rules
You can also create custom rules for specific apps. Maybe you want to allow an app to connect only to certain domains, or block it from specific regions. Portmaster gives you that level of control through per-app settings. You can do this by selecting the app from Portmaster, switching to its Settings tab, and then scrolling down till you see the Rules section.
The Safing Privacy Network (SPN) with Portmaster Pro
Portmaster follows a freemium model. All the above features are available with the free plan, but if you subscribe to their Pro plan at $9.90/month, you’ll get access to the Safing Privacy Network (SPN)—a VPN that offers Tor-like features and routes each connection individually using the onion encryption. This can potentially improve connection speeds by automatically picking exit nodes close to your destination.
That said, I personally stick with the free plan since I already use ProtonVPN, and it’s much more affordable.
How to install and set up Portmaster on Windows
Installing Portmaster is extremely straightforward. Head to Safing’s website and download the Windows installer. It’s a standard executable file—just double-click it and follow the installation wizard. The installer will handle everything, including setting up the necessary network drivers that Portmaster needs to monitor your traffic.
Once installed, Portmaster will launch automatically and walk you through a quick setup process. You’ll be asked to select which filter lists you want to enable—things like blocking trackers, malware, and phishing sites. I recommend enabling at least the malware and phishing lists. You’ll also choose your preferred DNS provider (Portmaster supports DNS-over-TLS and DNS-over-HTTPS for encrypted DNS queries).
The setup takes less than a minute, and once you’re done, Portmaster runs in the background, monitoring all network activity. By default, it starts automatically with Windows, so it’s always protecting your system. You can access the Portmaster interface anytime through the system tray icon.
Portmaster gives you full visibility into what your apps are doing online and the ability to block anything you don’t trust. It’s free, open-source, and simple to use, making it an excellent choice for anyone who wants to take a more active, hands-on approach to privacy and cybersecurity.
