There r many counter measures against the missiles, (flares,chafes , gatling gun,counter missiles etc) . We have to wait and see how they work against Brahmos.
This is how a missile sees a ship...
Each geometrical facet represent a unique radar reflection point on said ship. The missile does not see a 'square' or 'rectangle' or 'triangle' but voltage spikes and all these spikes are in a cluster against a background. The above image was created to give the readers a reference they can visually relate to a shape we know as a ship with all those radar reflection points highlighted.
Now onto chaff defense...
A ship in less than five seconds can launch enough chaff canisters to totally blanket a missile's radar view. The problem for the defense is
WHEN to launch those canisters. The goal for the defense is to create that electronic blanket
BEFORE the missile can create in its own electronic mind a composite image of a 'ship' based upon those unique radar reflection points. So again...The problem for the defense is
WHEN to launch those canisters.
Once the missile created that composite image of a 'ship', chaff's efficacy as an electronic defense rapidly diminishes because the ship is moving too slow compared to the missile to avoid impact. It does not matter if by that time the missile's radar is blanked out. The missile already recorded a cluster of radar reflection points in an x-y-z coordinate and will head for that spatial location. It may miss or it may not but odds are better than %50 that it will impact the ship, possibly in an important area. The missile designer may incorporate some fancy algorithms based upon those radar reflection points to sort of guess what is the ship's most important structure and program the missile accordingly.
The best chaff defense against a radar guided missile is to create that electronic blanket
BEFORE the missile successfully create that composite image. Chaff must be launched at the correct time lest they fall too soon, thereby exposing the ship at the worst time. On the other hand, chaff is cheap and does not take up much storage space. If the fleet or ship is sufficiently forewarned, it will take a lot of missiles to exhaust the ship's supply of chaff.
For flare defense against infrared sensor equipped missiles, the same tactic applies. The problem for IR sensor technology is that currently it is very difficult to create an IR sensor that is as capable of distinguishing distinct IR emitters as clear a radar emitters from the same body. This is a cost versus benefit issue and another point for discussion. Suffice to say that it is too costly to incorporate that level of IR sensor technology into a missile.
The Space Shuttle example below illustrate some IR emitting points...
Spaceflight Now | STS-119 Shuttle Report | Discovery's re-entry to collect hypersonic research
Nowhere as detailed as radar emitting points. This is why radar guidance remains the preferred method.
Ya manoeuvrings affect the range to some extent but not the way some think.
The readership would like some elaboration.
Also it only follows a straight path after it selects the target. I dont have any idea if there is such missile in the world. Please correct me if there is one.(don't exaggerate please)
All cruise missiles does that to maximize their kinetic energy.