The hotfix for this was to be released by end of March, but it will be a wee bit later than that - 1 to 2 weeks into April. SB10014 will be updated when the fix is available.
Patch 5 does not contain a fix for this vulnerability.
The hotfix that addresses this vulnerability will be a mandatory fix, since it addresses a vulnerability.
The DAT files only stop the known threat, it does not stop the exploit from being used.