Grand Theft Auto III
Near Love Media building, there is a pipe in the ocean that is cut-out, the pipe also bears the caution sign reading Hot Steam. Steam does explode in water. This hints that this may be the work of terrorists to detonate an immense explosion.
Grand Theft Auto IV
The terrorist threat frequently mentioned in GTA IV is never officially experienced by the player, rather it is the recent strict legislation and the foreboding, sense-of-emergency mindset held by multiple NPCs that highlights the prominence of terrorism in Liberty City.
Shortly before the events of GTA IV, a vaguely described terrorist attack took place in Liberty City. Terrorism is mentioned numerous times throughout the game, including in news radio reports and on websites, most notably during the mission, Rigged To Blow, where a police dispatch officer can be heard over a police radio warning responding units that the explosion at the garage could be a possible terrorist attack.
It is likely that the terrorism theme of GTA IV's Liberty City was intended to reflect post 9/11 America, attempting to create a humorous caricature of people's fear-of-attack mindset and their tendency to take it too far.
It is possible that a terrorist threat never existed in GTA IV's Liberty City, with the City's various criminal undergrounds being behind a supposed "attack" like the mission Rigged To Blow being a prime example of this. This could be Rockstar's attempt at a further subliminal comedic jest, highlighting the media's tendency to spread potentially false accusations in an attempt to gain ratings, fueling people's fear and leading to very serious government legislation.
As a result of the Terrorist Attack, during the early parts of the game, a segregation of the city's boroughs is in place with a heavy police presence on bridges linking boroughs, forming roadblocks with their cars and additional concrete barriers. If players cross any roadblock before the segregation of that particular borough is lifted, they will attain an instant 6-Star wanted level.
After completing the mission Blow Your Cover, the mayor caves in under public pressure and partially lifts the borough segregation, opening up Algonquin to Bohan, Dukes and Broker. After completing the mission Three Leaf Clover, Alderney is at last opened to Algonquin, effectively ending the borough segregation of Liberty City. This however seems strange since a successful bank robbery would only fuel people's fears and it would not be long before desires to segregate at least part of the city soon arise again.
Grand Theft Auto: Chinatown Wars
Players have reported seeing random explosions around Liberty City. These range from gas stations exploding to cars being set on fire. There are also reports of men armed with flamethrowers and guns causing chaos on the streets. They are hostile to all NPCs, including the player. It is thought Rockstar added these mercenaries as an easter egg, referencing several real-life terror attacks and to reflect Liberty City's chaotic reputation; as reported in newspapers, websites, and news reports in other Grand Theft Auto titles.