Under the options menu, in firewall configuration is it best to use the upnp setting or go for the port forwarding. I have tried both and both seem to work so, which is the best to use bearing in mind security issues. I'm not really a techy so can't understand technical language too much.

AFAIK they should be equivalent. UPnP means LW is able to communicate directly with the modem/router to open a port. Whereas manual port forwarding is needed when there's some communication problem or the device has no UPnP ability. Both will still have NAT (firewall) support for all other ports.

As far as LW's abilities with UPnP, I believe Ultrapeer mode works best with manual PF (this was not the case with LW 4.8)

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Thanks. So either will be just as safe as the other.