In one month, VMware will end all active support for ESX and ESXi 4.
The software is currently beyond "General Support" and in a phase VMware calls "Technical Guidance". During that phase of support it is possible to log support calls and Virtzilla supports existing patches but doesn't issue new ones.
Technical Guidance ends on May 21, 2016, after which only self-help will through VMware's knowledge base and community will be available. ®