The ‘alert’ was a humorous way to give advice to citizens on how to prepare for such real threats as hurricanes, earthquakes, pandemics and terrorist attacks.

Homeland Security issues ZOMBIE warning! Actually, it’s part of a preparedness campaign for disasters.

CDC guide to surviving a zombie attack.
If zombies take over, the government wants you to be prepared.
The Homeland Security Department warned citizens on Thursday that the “zombies are coming,” and urged them to be ready for a walking-dead apocalypse, The Associated Press reported.
The zombie “warning” is part of a public health campaign calling for citizens to be ready for disaster — to know to stock up on food, batteries and water, and to keep extra changes of clothes and medication on hand.
Of course, those same preparations will also come in handy in case of a hurricane, earthquake, pandemic or terrorist attack, and that’s the idea behind the campaign.
In an online seminar, emergency planners were told to use zombies to get their point across that emergency preparation — for anything — is important.