modus_operandi writes: (via FARK.com): Clever malware authors have come up with a way to disguise malicious executable files as innocuous data types by writing the file name backwards. On May 11, analysts at Norman ASA (anti-virus software vendor based in Sweden) published details of the exploit in "The RTLO unicode hole — sequence manipulation as an attack vector". The trick is accomplished by using Unicode control characters such as 0x202E (right-to-left override) and 0x202B (right-to-left embedding). Although the payload is likely to be targeted at users of Microsoft Windows operating systems (which rely on filename extensions to determine whether a binary is executable) the exploit also works on any operating system which handles Unicode correctly. That means Linux and UNIX-based operating systems, including Mac OS X, will also be fooled into displaying a deceptive filename. Luckily, it is not possible to set chmod +x as a default in your umask! Could this technique be used in other, heretofore unsuspected, social engineering attacks?