The car changes security for people as individuals, for society and for civilization; whether for the better or worse depends upon perspective.
WOMEN AND DAILY HARASSMENT. Women mostly are less secure than men on the streets or public transport; they encounter less harassment driving a car and value the metal or glass armour between them and would be assailants. But the car culture reduces everyone's, but women's and children's particularly, security against serious assault when they are not in a car because there are fewer people on the streets, and their assailants are often car-bourne. Society, not vehicles, ultimately secures travel, and the car helps to break this down; but for car users the car does give an individual some empowerment by diminishing nuisance value harassment and some vulnerability when moving around on their own.
HOOLIGANS, LOUTS, OFFENDERS OF OPPORTUNITY OR IMPUNITY. A minority of car drivers and passengers display all the evils of "mobility culture" in random assaults upon pedestrians, these include vocal attempts to shock, verbal abuse in passing, throwing water, food, cartons or even potentially lethal metallic objects from moving vehicles. Pedestrians see many more cars than drivers do during a trip so even a small percentage driver delinquency results in a near certain harassment for the isolated pedestrian. At night in warmer months the harassment rate is so high one should walk on the side toward oncoming traffic rather than letting them approach unseen from behind, thus reducing their time and surprise factors. A smaller minority are on a near homicidal power trip and force pedestrians to run by accelerating or swerving towards any who cross the road in front of them; instead of maintaining speed or slowing. It is the getting away with it, the car's main "security", that brings out the delinquent tendencies in many otherwise restrained people, this group display the sense of diminished reality and responsibility that motivates most hit and run drivers (more 1).
GANGSTERS AND ORGANIZED CRIME. Obsessive car culture is now a consistent theme of all the world's criminal classes, gangsters were the earliest adopters of automobile technology, and the attractions of the car for criminals are obvious; it affords a quick getaway from a robbery, bashing, killing or any other crime, exemplified in the drive-by shooting. The car offers criminals a much greater carrying capacity than pedestrian activity, if the crime is murder it hides the body, if sex slave trading or other kidnapping it conceals the coercion being applied, if robbery it hides the loot, if armed robbery it hides the weapons until needed, and stolen cars are used in ram raids to smash through security grills, reinforced windows, gates, barbed wire fences or other "security" measures. Of course cars are also very useful to terrorists.
THE PRIVATE ARMS RACE. Cars are frankly dangerous because of collisions; but being chary of the danger will get one sneered at by those most scared even while their fear drives them to seek safety in bigger and bigger cars. Their kind of unilateral security, the "Volvo effect"(more 2), makes others less secure around them, so the danger causes a private arms race that dominates the roads. Those on bikes switch to motorbikes to escape life threatening near misses as they are overtaken, those on motorbikes switch to cars after alarming cutoff episodes, smaller cars switch to sedans, those in sedans switch to SUVs or an increasing number are discretely converted into armoured cars. The only limit on this knock on effect up the scale of violence and ecological destruction so far has been the cost of fuel, without which one might already have seen turretless tanks as "safe", "family cars". Like all wars this armour race is expensive, not just of money; human carnage is quickly cleaned up, chronic injuries vanish into quadriplegic and brain damage wards, animal corpses only litter the streets for the first generation of full scale car culture until they're all killed off or locked up; but the excessive consumption of resources costs the biosphere itself.
GLOBAL DANGERS - The car leads consumerism's assault on the biosphere and this assault is increasingly degrading the basis of our biological existence, the biosphere's viability, at least to support human life, it contributes to all major dangers, resource shortage, water shortage, land degradation, overconsumption etc. Despite the "think globally act locally" mantra, people largely don't know how; strategic aggregated levels of thinking only ever intrude upon a minority of consciousness' in an everyday way, and in even fewer do they inform their actions (see Tragedy of the Commons). But this sizable minority know that the car is eliminating our future, the thing which gives security meaning and purpose; and that there is ultimately no greater insecurity.