What are macros?Edit
Macros automate frequently used tasks to save time on keystrokes and mouse actions. Many were created by using Visual Basic for Applications (VBA) and are written by software developers. However, some macros can pose a potential security risk. A person with malicious intent, also known as a hacker, can introduce a destructive macro in a file that can spread a virus on your computer or into your organization's network. (Source: Microsoft.com)
Macros in Arena.Xlsm are safe and don't do anything to your computer. Arena.Xlsm uses a lot of macros to accomplish gameplay within a spreadsheet. These macros do fun video game stuff rather than boring Autosum stuff!
How do I enable macros?Edit
The method for running macros will vary depending on what version of Microsoft Excel you are using.
Excel 2008: Sorry, this version of excel is not compatible with Arena.Xlsm because it cannot run VBA macros.
Excel 2011: Sorry, this version of excel is not compatible with Arena.Xlsm because it does not support ActiveX controls.
Excel 2013: Microsoft Excel Help Page for Macros