Currently, Yara is not in the repository. Yara allows for scanning for known signatures of shellcode and other malware behavior in malware analysis. It is also required for the Volatility Yara scan plugin (which currently is inoperative because Yara isn't in Kali). It is open source and allows for free redistribution. Yara is an indispensable tool in the malware analyst's toolkit.

https://code.google.com/p/yara-project/