Starting February 1st, 2025, many clients have begun experiencing degradation in JxBrowser’s startup time on Windows. The root cause of the issue is a recent Windows Defender update.

UPD: February 11th, 2025: the original issue is no longer reproducible after the Windows Defender update 1.421.1831.0.

UPD: February 5th, 2025: we have released JxBrowser 7.42.0 and JxBrowser 8.3.0, addressing the issues caused by the Windows Defender.

After upgrading to JxBrowser 8.3.0 or 7.42.0, it’s no longer necessary to roll back the Windows Defender’s update, or whitelist the directory with Chromium binaries.

What happened 

Every time JxBrowser starts, it verifies the integrity of the Chromium binaries. The verification takes 100-200ms on an average machine.

After the Windows Defender update 1.421.1630.0, the verification time increased to several minutes.

The root cause 

This section was added on February 6th, 2025.

Every time JxBrowser starts the main Chromium process, it checks if the necessary Chromium files exist and are valid. We identified that Windows Defender intervened only when we checked the existence of a specific subset of files.

The files in question are *.pak.info files, which store localization data. These files are a part of any Chromium, Edge, or Google Chrome distribution. Following the problematic update, Windows Defender began intervening whenever any application attempted to open these files, causing the slowdown.

To check if the file exists, we used the java.nio.file.Files.exists() method. This method, in turn, called the native CreateFileW() function requesting access to read the file, which triggered Windows Defender.

How we fixed the issue 

This section was added on February 6th, 2025.

We moved the checking mechanism to a native executable and ensured that the CreateFileW() call requests access to only read file attributes, not the file itself.

We want to thank our wonderful clients who reported their findings and helped us to find the solution.

Whitelisting Chromium binaries 

As of February 5th, 2025, it’s no longer necessary to whitelist the directory with Chromium binaries, or to roll back the Windows Defender’s update, or Instead, upgrade to JxBrowser 8.3.0 or JxBrowser 7.42.0.

If you can’t upgrade JxBrowser, you can address the situation in two ways:

  • Add the directory with Chromium binaries to the whitelist.
  • Rollback the Windows Defender update.

To add the binaries directory to the whitelist:

  1. Locate the Chromium binaries as described here.
  2. Go to Start → Settings → Update & Security → Windows Security → Virus & threat protection.
  3. Under Virus & threat protection settings, select Manage settings.
  4. Under Exclusions, select Add or remove exclusions.
  5. Select Add an exclusion, and then select the directory with the Chromium binaries.