Security patches

There are 2 classes of 'critical' updates.

For security updates, 'critical' means that there is an open hole that will easily allow a virus or hacker to have access to the affected systems.

When a security update is marked as 'critical', it should be installed ASAP.
The hole is usually either very big, or has been widely disseminated among the hacker community.

For other 'critical' updates, a problem has been found with the program code that can cause a fatal error, loss of data, or prevent hardware from operating properly.

Chas