1. How can you tell if you have the virus?

Kaspersky (an antivirus vendor) have a stand-alone detection tool, available from their site See: http://support.kaspersky.com/viruses/utility - Flashfake removal tool; Further information about the tool is available from their news section: http://www.kaspersky.co.uk/news?id=207576489

Apple have released updates that come through Software Update for Snow Leopard and Lion. These detect and remove some of the variants of Flashback:

2. How to stop your machine becoming vulnerable?

- for owners of machines that do not get operating system updates (PPC macs)

You should disable all browser plugins that are a specific risk. However, because these versions will remain unpatched, the entrire rest of the operating system is still a risk. It would be advisable to switch to Debian PPC, to continue using this hardware with a supported operating system.

3. What other precautions can you take?

It is highly advisable that an antivirus product is installed on your Mac. Sophos Home Edition for Mac is available for both Intel and PPC Macs: http://www.sophos.com/en-us/products/free-tools/sophos-antivirus-for-mac-home-edition.aspx