GitHub recently improved its SSL setup by removing RC4 support:
RC4 has a number of cryptographic weaknesses that may be exploited, impacting the security of your data. More details about these vulnerabilities are listed in the current IETF draft.
If you are using Internet Explorer on Windows XP, you will no longer be able to access
github.comonce this change takes place. Windows XP only supports outdated SSL ciphers, is no longer supported by Microsoft, and contains a known critical security problem in its SSL implementation.
Since this breaks the site in Internet Explorer on Windows XP, I assume that sites that are accessible with IE on Windows XP must support RC4 ciphers.
Does this mean that those sites are not as secure as possible?