Aggro, or aggression, is how the infected in an area behave in response to a survivor. Aggro is one of the most commonly heard terms in Dead Frontier. It refers to the amount of attention the zombies in the Inner City give you. As aggro increases, so does the number and speed of zombies.

Causes

It is thought that aggro increases as you go deeper into the city, but it is only the overall amount of infected that is higher, meaning there are more that will attack when aggro is raised. Aggro is increased by making noise; the bigger and noisier the weapon, the faster the aggro level will be raised. Aggro sometimes appears in some missions so be alert when doing missions. As aggro increases, there will be a larger zombie presence, meaning that zombies will rush more quickly, and zombies may even swarm a player. Melee weapons do not increase Aggro nor do they attract onscreen zombies; however, chainsaws will attract onscreen zombies, and cause aggro equivelant  to a pistol or rifle and if they run for too long, can cause aggro while if a player kills too many zombies with a silent melee aggro will occur, usually in yellow, orange, red and black zones. Pistols, rifles, and submachine guns cause lower amounts of aggro, but will gradually build with continued use. Shotguns, Explosives, Assault Rifles, and Heavy machine guns and Miniguns increase aggro by large amounts and attract large numbers of zombies, both offscreen and on. 

Occasionally, aggro will increase without any provocation. This phenomenon is called an "Aggro Spike" and is not a coding bug. Except for the "regular" burning zombie, bosses will carry an Aggro Spike. Sometimes, it can be temporarily reduced if the player goes off screen at the beginning of the spike (i.e., switching areas, entering AFK, etc.). Players can also attempt to fight through the spike, which although difficult, is possible. Take caution, however, as bosses may accompany Aggro Spikes.  Chances of Aggro Spikes are greatly increased in Yellow, Orange, and especially in Red zones. Aggro Spikes can attract bosses and will end after a long period of time. This being the case, it is best to avoid Aggro Spikes when looting. If entering AFK to escape a horde or small amounts, they'll continue to chase and attack you after you come out of it. Aggro can only be stopped if a player:

1. Refreshes the page 3-5 times
2. Crosses 3-5 different blocks

Also, aggro keeps on increasing (see below) even though you haven't fired a shot or used a chainsaw. It could be due to aggro spikes, but aggro will increase regardless of whether you use melee or not. Which is why sometimes, when you've been looting for a long time and fire just a few shots, to kill a bloat, for example, and there is a massive amount of aggro suddenly, it is because the aggro has been building up.

How Aggro Works

The best way to explain aggro is to think of it like a digital meter: when aggro increases the number increases. If you shoot a lot with a gun, the number increases and according to that number a certain amount of zombies spawn . If you kill all the zombies ( e.g : At max aggro , 40 zombies spawn total ) then the number drops down again . Aggro increases upto a certain point ( depending on where you are ) where it'll either spawn endless aggro or a boss along with aggro .

However aggro increases the longer you stay in the Inner City ( Which is why you have aggro spikes or if you stay too long in a Personal Outpost , there'll be a Personal Outpost Attack ) . So using melee wont guarantee that there will be no aggro after a while , but melee keeps the aggro down the longest ( a exception to this is chainsaws ) . It is recommended to cause aggro after staying in the IC after a long time ( 2 days minimum ) as the aggro which has been building up will drop again .

Effects

The effects of increasing the aggro level is not always immediately seen. A player might think he/she has no aggro and will enter a building to loot it or to create a Personal Outpost ( PO ) and he/she will see zombies spawning in and sprinting towards the survivor . Going outside will show there is no aggro . At a certain point many infected will now be speed walking or running at you in packs ( on the streets ) . The further from the Outpost you go, zombies will become more frequent, and stronger infected will appear.

High aggro in 3D is characterized by large numbers of very fast zombies. Zombies will charge directly at the survivor with maximum speed, trying to kill him or her. If they cannot reach the survivor directly, they will change directions in an attempt to get around whatever is blocking them. (But if they are behind a high fence, it's best to keep their attention by firing at them so that they don't figure out how to go around and attack you.)

Chainsaws, Machine Guns, Shotguns, and Grenade Launchers provide a survivor with excellent firepower, and fences and objects may be very useful objects while escaping packs of zombies. Still, if you're not properly armed in the situation, run away.

Sometimes the aggro increase is not easily seen outside you will be ignored by other zombies but once you go inside a building, zombies will start spawning through doors and from stairs and are sprinting towards you.

Reaction

Player reactions vary, because there are those who want aggro so that they can gain EXP (grinders), and those who don't because their goal is to find things to get money or items (looters).

Aggro on a loot run or a scouting mission is undesirable, as it obviously makes it more difficult to search bodies, cars, etc. Using loud weapons, such as Shotguns, Machine Guns, Chainsaws, or Explosives, will cause aggro and should be avoided unless absolutely necessary. Causing aggro on a loot run is sometimes met with disgust by other players. It is advisable to loot in Single Player, because other people in the party may start to use firearms, and thus attract more aggro.

A few select players will want aggro, whether for gaining EXP, or just for a good fight. For these types of gamers, an idiot proof equation has emerged:

Players + Noisy Weapons = Aggro = Zombies

Weapons + Skill + Zombies = EXP

Leveling

Should a player choose to level or grind in a high aggro scenario/environment, he or she must keep a few important things in mind in order to be successful.

Solo Aggro/Team Aggro - This is important, as an aggro situation differs drastically from when you are on your own and from that when you are together with one or more players. For example, In Solo Aggro, the most ideal situation is when you are fighting a horde of zombies from one direction. It is easy to side step or run even in tight areas, especially if the zombies are relatively slower than you. However in an aggro situation where there are 2 or more players, there are instances that each player has his/her own group of zombies chasing him/her. This can be risky at tight areas as there are moments when zombies following one player suddenly shifts attention to another player, catching him or her off guard.

Watch your Energy - Since the number of fast moving zombies increase in high aggro, chances are you will expend more of your energy in running . So conservation of energy is the most important thing of all. Once you deplete your energy, it will be more difficult to avoid attacks, especially at cases where exceptionally faster zombies are swarming from multiple directions.

Fight what you can kill - Though not impossible, it is cumbersome to eliminate a boss or a continuous horde of zombies if you are not properly equipped, built, and skilled. It is always wise to fight within the scope of your capability and resources.

Note : If you want to kill a boss , but want to ignore the other zombies , either take the boss to a lonely place or keep on moving .

Look out for others - Some like aggro, some don't. Always be considerate of those who don't. When you want to induce aggro, make sure you do it in situation where others won't be caught off guard and put at risk.

Notes

• Some zombies will show up at certain points randomly even without aggro.
• Players can cause aggro on purpose by shooting excessively with a noisy weapon. Be warned, though, all players in the vicinity will experience the increased aggro.
• Zombies move much faster while in higher aggro state.
• Zombies have the ability to push other zombies thus increasing the movement speed of that zombie. This is a huge problem if the aggro raises and the player has low agility.
• Survivors should use melee weapons as their primary weapon during loot runs.
• Bosses can be attracted by heavy aggro if you're in a boss spawn zone.
• Be sure to have high agility.
• Aggro increases even if all your weapons are melee. Meaning, even if you never shoot, or use a chainsaw, aggro will still increase.
• Aggro spikes refer to a sudden increase in aggro.