---
title: Trojan malware
description: Learn about how trojans work, deliver malware do your devices, and  what you can do to protect yourself.
keywords: security, malware
ms.prod: w10
ms.mktglfcycl: secure
ms.sitesec: library
ms.localizationpriority: medium
ms.author: dansimp
author: dansimp
ms.date: 08/01/2018
---

# Trojans

Trojans are a common type of malware which, unlike viruses, can’t spread on their own. This means they either have to be downloaded manually or another malware needs to download and install them.

Trojans often use the same file names as real and legitimate apps. It is easy to accidentally download a trojan thinking that it is a legitimate app.

## How trojans work

Trojans can come in many different varieties, but generally they do the following:

- Download and install other malware, such as viruses or [worms](worms-malware.md).

- Use the infected device for click fraud.

- Record keystrokes and websites visited.

- Send information about the infected device to a malicious hacker including passwords, login details for websites, and browsing history.

- Give a malicious hacker control over the infected device.

## How to protect against trojans

Use the following free Microsoft software to detect and remove it:

- [Windows Defender Antivirus](https://docs.microsoft.com/windows/security/threat-protection/windows-defender-antivirus/windows-defender-antivirus-in-windows-10) for Windows 10 and Windows 8.1, or [Microsoft Security Essentials](https://www.microsoft.com/download/details.aspx?id=5201) for previous versions of Windows.

- [Microsoft Safety Scanner](https://www.microsoft.com/wdsi/products/scanner)

For more general tips, see [prevent malware infection](prevent-malware-infection.md).