Last week, a couple of guys were fired from the company I work for; all of them had access to sensitive information.
One of them erased all the e-mails from the mail server, sent a massive e-mail to most of our customers, insulting them, and telling them not to do business with us because "We suck". Literally.
The system administrators failed to remove their credentials for the servers when they were fired, a very common mistake unfortunately. The current system administrators do not seem to know what to do under this scenario. Neither do I to be honest, and I would like to know what is the normal procedure to follow in case of a security breach, so I can make a recommendation to implement it in the company.