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If you see a warning like the one below when downloading the Mac version of BikeCAD Pro, do not be alarmed. The file is not damaged. Apple's Mountain Lion operating system (OS X version 10.8) makes this sweeping statement about any app that was not downloaded from a very limited list of sites. To get around this, go to your Mac menu at the top left side of the screen. Choose System Preference >> Security & Privacy and then "unlock" this window. Under "Allow applications downloaded from:" choose either Anywhere.
Once you've installed BikeCAD as described here, and launched the program once, you can restore your security settings to the previous values.