There aren't any really. To truly test a system's security, you need to have something running ON the computer.
As far as I'm concerned, all sites like (and including) Shields Up are scams. They're designed to try and scare you into buying some associated product or service, just like all those third party firewall programs for Windows craft messages that make it sound like the Mongol Hordes are massing with the Visigoths at the gates, and they're just waiting for the slightest of openings. They have to try and convince you they're adding some kind of value somehow, even though they're really not.
You're running Mac OS X, which is a good first step security wise. Virtually eliminates the threat of viruses and malware. More than that, it's based on FreeBSD, so assuming Apple did the smart thing, the firewall in Mac OS X will be based off of FreeBSD's ipfw, which is widely regarded as one of the best around. So then there's that. Which then leaves you primarily with making sure you install security updates when they become available, avoiding any programs with a known history of security issues, and then making sure to do simple things like not opening strange email attachments, clicking on any random link someone sends to you, realizing that that Nigerian oil tycoon really didn't select you to help spirit his vast fortune out of the country upon his death, not going to the seedier parts of the Internet and then bragging about how no one can hack your computer... You know, simple, fairly common sense, sorts of things.
Computer security is probably 90% user actions, and then you have a couple of programs that kind of help pick up some of the slack since we can't maintain a high level of vigilance indefinitely. You shouldn't depend on programs to do the majority of the work. That's a great way to be surprised one day, and not in a good way.
Can anyone suggest a reputable site that could test my system's security please?(along the lines of Shields Up! - on which I have found starkly varied opinions).
Many thanks
AOx

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