Great to hear your kid is into PC gaming. He'll learn a lot about computers if he sticks with it; ideally building his next one after this.
As for the rig you posted, it looks good except for the graphics card, which is
weak. Typical for pre-made systems to have a good processor and ample memory, but topped off with a "meh" GPU.
I'd also look at a mid-tower at the very least (more spacious, and that'll be more upgrade-friendly down the line) and any GTX 6 series graphics card from Nvidia, or 6870 or up from ATI/AMD. Reference the chart in the link above for these and choose whichever your budget affords you. He should be set to run everything for a few years then.
A free, unobtrusive antivirus program like Avast or AVG plus a maintenance tool like Advanced System Care or CCleaner is all anyone needs for Windows to keep running smoothly and safely. The key is to avoid the darkside of the interwebs lol. Its been revealed on hardware sites that Windows 7 is more secure than Mac OS's but the difference is the millions of viruses that target Windows and not Macs.