Secure Sockets Layer (SSL) is no longer considered secure due to known vulnerabilities and cryptographic weaknesses. Modern standards require the use of newer versions of Transport Layer Security (TLS), and similarly, DES is deprecated for strong security. However, the best and most universally referenced example is SSL, as major industry and regulatory bodies recommend disabling SSL entirely in favor of TLS 1.2 or above.
Reference: ISA/IEC 62443-3-3:2013, Section 4.2.3.7 ("Cryptographic protections"); NIST SP 800-52 Rev. 2.