Computer Clock on Military Time

Ever since I had some malware issues, my computer clock has been acting weird. For a while it stayed an hour behind every time I turned the computer on. Now, for the past week or so, it shows up on military time!
How do I fix this? I know how to fix it manually, but I'd like to make it stop doing this in the first place. I'm using Windows XP.

 

24 hour clock is a superior clock to learn as there is no AM/PM
Right clicking the clock should open clock settings. From there select 12 hour clock and click to auto update time online. If you still have problems recheck for malware