According to
https://wiki.centos.org/HowTos/EOL, CenOS 5 have to EOL (End of Life) since 31 Mar 2017.
Impact for EOL, certain repos for CentOS become 'HTTP Error 404: Not Found'. At this moment, may impact to CentOS and IUS repos.
So, better to CentOS update from version 6 or 7.