Windows 7 with Defender

Using TeamViewer 11 I have 3 Windows 7 computers and they only are using Windows Defender for Anti Virus. I have Windows 8.1 and Windows 10 they also only use defender as does many of my Servers.  But on the Windows 7 computers I get a Yellow waring on the computer which Team Vewer believes there is no anti virsu program running.

Why on other then Windows 7 does this not detect Defender

Thakn you

Tom