Thanks for the positive review!
1. Yes, the malware issue has been fixed. We migrated our server and updated server side code that had allowed a security hole. No code on your end needs to be updated.
2. The shortcode in wordpress copies in some HTML and a script tag that might look like the following (varies a bit depending on what calculator you loaded)
<div class="cp-calc-widget" data-calcid="1766" data-anchor="4"></div><a href="https://www.calculatorpro.com/calculator/loan-calculator/">Embed this Calculator</a><script src="https://www.calculatorpro.com/wp-content/plugins/calcs/js/widgetV6.min.js"></script>
The javascript file loaded by the script tag is a small file that injects the calculator HTML (along with some CSS) into your page. We have it set up this way so that if we need to push out an update for browser compatibility, we need only update our script file and then that script files starts getting used the next time a browser loads it.
When a user actually clicks “Calculate” an ajax request is sent off to our server where the answer is computed and sent back. Only the users’ inputs to the calculator (along with basic required elements like the calculator ID) is sent to our server for this calculation stage.
3. Yes, our plugin is compatible with WP 3.5.1.
Please also check out our site at https://www.calculatorpro.com to see some of the customization features we’ve added there (like translation, for instance)!