The Purple server will be rebooted Thursday between 21:00 and 23:59 BST on Thu 24th May 2018 to patch a new variation of the spectre vulnerability.
This vulnerability meant that a local attacker could read private data out of memory.
The outage should only last around 5 minutes while the systems reboots.
Update: 22:33 - This work is starting now
Update: 22:42 - This work has now been completed without incident.