How is misidentifying my browser good for security and privacy?
Almost every major release of both leading browsers has contained bugs that allow malicious servers to compromise your privacy and security. Known bugs are quickly fixed, but millions of copies of the affected software remain out there, and yours is probably one of them. The header that normally identifies your browser tells such servers exactly which attacks to use against you. By misidentifying your browser you reduce the likelihood that they will be able to mount a successful attack.
