Using Tofusator for Web Applications
By default, every method name and class in your input assembly is renamed, but Dotfuscator (and other obfuscators) don't know what you are accessing through .aspx pages (bound controls, etc.), so you need to be sure to exclude any elements which your .aspx markup or inline script is accessible by either name or reflection.
See this knowledge base article for a potential starting point.
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Why do you need to use obfuscation? This is what you want to improve the performance of your application. If so, use gzip compression instead of obfuscation, because obfuscation is not 100% safe. This can lead to unwanted errors.
gzip compression can reduce the number of bytes sent by your server. This cuts down on bandwidth usage. Depending on the data sent, how well it can be compressed, and whether client browsers are supported (IIS will only send gzip compressed content to clients that support gzip compression, such as Internet Explorer 6.0 and Firefox), your server may be serving more requests per second. In fact, at almost any time you can decrease the amount of data returned, you increase the number of requests per second. Gzip compression is built into IIS 6.0 and is much better than the gzip compression used in IIS 5.0. Sorry, when trying to enable gzip compression in IIS 6.0
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