Google users searching for the term “Zerg Rush” had a big surprise; the colored letters “O” turn into aliens that devour the page – and the users could click on the little “aliens” to kill them.

The hidden “Easter Egg” is a reference to the space strategy game Starcraft, where using a “Zerg Rush” with the game’s “Zergling” creatures is often a winning strategy.

Google has a long tradition of hidden “Easter Eggs” – as well as its famous Google Doodles.

Even by Google’s standards, though, this joke is particularly geeky.

The “Zerg” is one of the races in a strategy game, Starcraft – and experienced players often rely on the “Zerg rush” to win games.

The verb “to Zerg” is now often used in other online games, meaning to overwhelm an enemy through sheer force of numbers.

The game Starcraft was released in 1998, but is still played today.

If you search for “Zerg Rush” on Google, the colored letters “O” turn into aliens that devour the page

Maker Blizzard entertainment says: “In the distant future, the newly formed Terran Dominion faces the arrival of two hostile alien races: the savage Zerg and the enigmatic Protoss. Gather resources and expand your forces to lead them to victory. The only allies are enemies. The only choice is war.”

You have to search from the Google home page to make the “trick” work, and it may not work in mobile browsers or some desktop browsers.

The gamer joke is similar to an earlier Google “Easter Egg”.

Entering “do a barrel roll” as a Google search prompted computer screens to do a 360-degree turn.

Google told ABC News: “Today’s fun query, <<do a barrel roll>>, was created by a Google software engineer with the primary goal of entertaining users – while showcasing the power of CSS3, a presentation feature of modern browsers.”

The phrase quickly became a trending topic on Twitter as users urged their followers to try it for themselves.

The feature can also be used if one searches the phrase “Z or R twice”, Google’s homage to the Nintendo 64 video game Star Fox.

The barrel roll maneuver in the popular 1990s game could be completed by toggling the Z or R buttons twice.