If you're looking to buy a Windows RT tablet, don't expect to be able to protect it with third- party antivirus or other security software. In fact, it seems that Microsoft may block third-party antivirus vendors from developing security solutions for Windows RT.
Microsoft won't allow such software to be sold on its online store, which is the only way to load applications onto Windows RT devices. Most security observers assume Microsoft will develop its own security solution for Windows RT.
Source: Readwriteweb