Trojan:Java/Classloader

Classification

Malware

Trojan

Java

Java.trojan.exploit.bytverify

Summary

The Classloader files are Internet Explorer (IE) homepage hijacker trojans that infect IE through malicous web pages, which host exploits targeting the Java classloader byteverify vulnerability in unpatched versions of IE.

Removal

Automatic action

Based on the settings of your F-Secure security product, it will either move the file to the quarantine where it cannot spread or cause harm, or remove it.

Suspect a file is incorrectly detected (a False Positive)?

A False Positive is when a file is incorrectly detected as harmful, usually because its code or behavior resembles known harmful programs. A False Positive will usually be fixed in a subsequent database update without any action needed on your part. If you wish, you may also:

  • Check for the latest database updates

    First check if your F-Secure security program is using the latest detection database updates, then try scanning the file again.

  • Submit a sample

    After checking, if you still believe the file is incorrectly detected, you can submit a sample of it for re-analysis.

    NOTE If the file was moved to quarantine, you need to collect the file from quarantine before you can submit it.

  • Exclude a file from further scanning

    If you are certain that the file is safe and want to continue using it, you can exclude it from further scanning by the F-Secure security product.

    Note You need administrative rights to change the settings.

Find out more

Knowledge Base

Find the latest advice in our Community Knowledge Base.

User Guide

See the user guide for your product on the Help Center.

Contact Support

Chat with or call an expert for help.

Submit a sample

Submit a file or URL for further analysis.

Technical Details

These trojans usually change the browser start page and search settings and download other trojan/spyware components on the system. These trojans are distributed on malicious web pages that contain references to the trojans. Usually the classloader files are in a .zip or .jar archive along with several other files.

Installation

The Classloader based trojans install themselves from a malicious web page that contains a reference to the trojan. The trojan uses a vulnerability in the classloader system of Microsoft Java runtime, that allows the malicious applet to break out of the sandbox, and gain same access as any other executable running with users permissions.

Payload

After being executed these trojans usually download executable components that are either further parts of the trojan or spyware being dropped by the trojan.

Note

Using the latest version of Internet Explorer and keeping up-to-date with the latest security patches is the easiest way to protect against possible infection from Classloader trojans, as this fixes the web browser vulnerabilities needed for the trojan to work.