tl;dr: jessenic found that by disabling the unnecessary Defender service on his Surface RT, his performance was dramatically improved. Details below.

Now, before you go around saying nonsense, here's the gist of the situation. Windows 8 and Windows RT have Defender, Microsoft's "security essentials" service, built into the OS. This does real-time scanning of files, processes, etc. on your machine. On the desktop, this is nice, because it gives you an integrated anti-virus/anti-spyware system and removes the requirement of needing third-party threat tools (unless you're paranoid or hang out on the darknet).

Windows RT also has this bundled. This is kind of bizarre, actually, as I would argue it's completely unnecessary, as Windows RT is ARM based, and only runs signed code (unless you jailbreak it), so if someone made ARM-based malware, it wouldn't run anyway.

It is theoretically possible that someone could trick you into running a powershell script with admin rights, but that wouldn't be covered by Defender anyway.

Point is, by disabling Defender, you can gain a huge performance boost on your Surface RT. Jesse claims his apps run instantly and without lag. Your mileage may vary, but I'd argue it's a tweak with trying.

Check out the steps over at XDA, and post there or here in the comments if it gives you any sort of noticeable performance boost.

No, this will not make your device insecure.