Microsoft has issued a warning to people not to open files with the rtf extension due to a vulnerability that Microsoft has just discovered that could enable a hacker to send you an email with an .rtf file attached that if you download will enable the hacker to take control of your computer. At the moment, although Microsoft has discovered the problem, they do not have a solution so they are advising people not to open such files and to consider disabling the opening of .rtf files. RTF is an acronym for rich text format files which is a file format Microsoft developed for use with Word software.
Microsoft has released a security advisory with more details about this threat and what you can do to reduce the danger. Here is a link to Microsoft’s security advisory about this problem: http://technet.microsoft.com/en-us/security/advisory/2953095. For now, the best course of action is to totally avoid rtf files.