It cannot be named as con because OS has some spl file named as con, so we cant... but we can do it by using a space or any invisible character before or after the end of con. Source: CoolInterview.com
Such files are considered to have an extension but no name. If the extension is known and the user has chosen to hide known extensions, the resulting file would have no name at all!
If you really want to create a file with a leading dot in its name, you are free to do so. You can do it from the command line or use your favorite file management tool. And then you can watch the file show up with no name and then observe the confusion that ensues. Maybe you're lucky and don't run any programs that freak out when a file has no name. If so, then more power to you. Source: CoolInterview.com
You can not use "con" as a name since the Operating System is using it for other issues like device name, ...etc, Also you can not use (PRN, AUX, NUL, COM1, COM2, COM3, COM4, COM5, COM6, COM7, COM8, COM9, LPT1, LPT2, LPT3, LPT4, LPT5, LPT6, LPT7, LPT8, and LPT9 ) in WinXP not giving you error but now with Win Vista it is giving you error message. Source: CoolInterview.com