It depends on what you are trying to do. If you are a digital artist, I can suggest Krita. It's really nice for painting and supports all sorts of pressure sensitive pens but you can just use a mouse or trackpad. I've had a crash or two so I save frequently, but otherwise very well featured. Krita is open source and multi-platform.
If you are using the ...
If your calculations are simple or the data is in columns, your best bet might be to use a spreadsheet program to plot the data. Excel plots data or the free suite called Open Office has a spreadsheet package called Calc. It will also plot data. If you want to plot an equation just define the x values and calculate the y-values from the equation.
There is an app called Malwarebytes that will scan your system for malware and viruses. It is currently very popular with Mac users. The personal copy is not free. It sales for one device for $3.33 per month or $39.96 per year. You can start and stop the app whenever you choose.