Windows Defender (first era)
This icon could be seen on the taskbar of Windows XP, Vista, and 8/8.1.
Microsoft Security Essentials
The launch of Windows 7 introduced a new antivirus software called Microsoft Security Essentials. The icon resembles a medieval castle with a blue flag sticking out.
Windows Defender (second era)
This logo was used on Windows 10.
This icon is being used today on Windows 10 and Windows 10X operating systems.
Microsoft Windows apps
3D Builder | Alarms & Clock | Battery Saver | Calculator | Calendar | Camera | Clipping and Annotation | Clock | Console | Data Sense | Defender | Fax with Scanner | File Explorer | Fresh Paint | Groove Music | Mail | Maps | Messaging | Movies & TV | Notepad | Paint | Paint 3D | People | Phone | Photos | Settings | Sticky Notes | Storage Sense | Microsoft Store | Tips | Wallet | Whiteboard | Windows Installer | WordPad | Xbox Console Companion | Xbox Game Bar | Your Phone