CentOS 6.8 was released this week. With a number of security and performance updates, it provides a more stable and secure experience for CentOS 6 users.
The CentOS Project currently is shipping version 7 of its operating system, but older versions all the way back to 5 are still supported. However, as CentOS is based on Red Hat Enterprise Linux (RHEL), it depends on the parent product for many of its important fixes and security patches. Red Hat is winding down support for version 5 and is currently releasing only crucial security patches.
Version 6 is still very active, and the latest release brings a number of bug fixes and updated packages. SSLv3 has been disabled by default. SSL 3 has been considered insecure for some time now, ever since Google released details of the POODLE exploit. There are newer protocols for secure communications which are less risky - you can read more about the issue here. As CentOS is a popular choice for Web servers, disabling SSL 3 is essential.
Cryptography has been strengthened, with many applications updating to support elliptic curve parameters.
ntpd (the network time protocol dæmon) has been replaced with a newer alternative named chrony. Chrony is a more sophisticated service with a lighter interface. It eliminates some of the features from NTP that are rarely used. At the same time, it reduces overall network traffic. It can collect time information from a wider range of sources, and it's faster.
Squid has been updated from 3.1 to 3.4. Squid is a caching Web proxy that allows administrators to control access to the Internet and reduce Web traffic by caching resources unlikely to change between requests. For instance, images and videos can eat up a lot of bandwidth. If the Web server sends the right header information, those files often can be cached. When everyone in the office wants to see the latest viral video at the same time, this can amount to a large volume of traffic. Squid can reduce the congestion, improve performance and cut costs.
CentOS is a popular choice for network-facing machines, such as Web servers, but there also are features for desktop users. Version 6.8 includes an updated version of LibreOffice, along with other recent desktop apps.
Although the support team is keeping version 6 alive, most new users should install version 7. Version 7 is stable and features a wider range of up-to-date software packages. 6.8 will be supported until 2020, but users will miss out on cutting-edge software from version 7.
CentOS is well documented, and you can read more about the changes in the documentation.