There are heaps of infected files being shared on the network. So you need to make sure that you're using a good AV program. Keep it updated & use it to scan all files that you've downloaded, before you open them.

Watch file sizes...be wary of files less than 2000 KB in size.
WARNING: Viruses on network you should be aware of!

The decision to share is up to you, but remember that this is peer-to-peer...if everyone chose not to share then there'd be nothing worth downloading on the network.
And you wouldn't be able to download the files that you want

If you're wary of sharing straight away then that's fine...once you've been using LW for a while then you might decide to start sharing. I hope so

To disable sharing, go tools > options > sharing & untick the folders that are set for sharing > apply > ok.