RC4 is among the older stream cipher suites anyway and there have been a number of practical attacks against it, including plaintext-recovery attacks. As computers have become more powerful attacking it is easier than ever. Microsoft’s William Peteroy said in a blog post that in light of recent research into practical attacks on biases in the RC4 stream cipher, Microsoft is recommending that customers enable TLS1.2 in their services and take steps to retire and deprecate RC4 as used in their TLS implementations. Microsoft recommends TLS1.2 with AES-GCM as a more secure alternative which will provide similar performance.
He said that more than 58 per cent of sites do not use RC4, while approximately 43 per cent do. Of the 43 per cent that use RC4, only 3.9 per cent require it. Disabling RC4 by default has the potential to decrease the use of RC4 by over almost forty percent.
Meanwhile Redmond is recommending that certificate authorities and others stop using the SHA-1 algorithm. Microsoft cited the existence of known collision attacks against SHA-1 as the main reason for advising against its use. After January 2016, Microsoft developers can no longer use SHA-1 in code-signing or developer certificates.