Few basic security info regarding virtualization

Hello guys,
I hope someone will clarify few things regarding antivirus protection with virtualized machines.

For example, I have windows 7 pro host machine on which Windows XP as guest OS is installed. On Windows 7 pro is installed security essentials which is updated regularly. Also automatic updates are enabled on the host machine.
However, virtual machine is Windows Xp and we know that since 2014 there is no official support by Microsoft. This includes security patches. If this guest XP OS is connected to a LAN network (bridge mode NIC on host machine), I guess this is a security risk and weak spot.

Can underlying host machine which is updated regularly prevent network worms or virus propagation or not?
For that point of view is it important if host OS has antivirus installed at all?

Thank you!

The xp is isolated so will be findable it won't be protected

Protection on the host provides a level of protection on virtual machines but it is not sufficient. It might have offered reasonable protection against malware as it existed 10-15 years ago, but not anymore. Modern malware has developed all kinds of methods of evading that kind of protection. Much modern malware can only be detected by active scanning on a live system, in this case the XP OS. Even then there are no guarantees. XP has known security vulnerabilities, and likely more that are not yet known, that will never be fixed. At the present time migration of malware to the host is difficult but you can be sure malware authors are working on it.

Thank you for the information. I thought this VM on a LAN network is a weak spot and possible trojan horse.