An attacker can use the differences between the application and the IDS as an unlocked, unwatched window to the prize. Signature-based NIDSs can have trouble dealing with the complexities of application interactions. The potential for evasion at the application layer is increasing because new protocols are becoming more complex with support for features like Unicode. Unicode provides a unique identifier for every character in every language to facilitate uniform computer representation of the world's languages. Unicode is managed by the Unicode Consortium and has been adopted by most information technology industry leaders.
Unicode support is available in many operating systems and applications.
The UTF-8 to Unicode transformation is algorithmic so that it can take place in code without resorting to lookup tables. UTF-8 URLs are supported by Microsoft Internet Explorer and Office 2000. Apache can be configured to support UTF-8, but is not by default. He pointed out that with the Unicode character set, it is possible that there could be multiple representations of a single character. There are also code points that may be used to modify the previous code point.