Systems claimed by players may develop Strategic, Industry and Military indices based on the activity of players in the system and the amount of time that they have held their system. Increasing these indices indicates that players are invested in their systems and thus the systems are harder to capture. This is reflected in the Activity Defense Multiplier. The higher the various system indices are the longer it will take for hostile to disable affected structures when using the Entosis Link module.
The maximum effect the system indices can have is a 6 times multiplier on the amount of time the Entosis Link module will take to fully attack a structure. Note that this does not multiply the cycle time of the Entosis Link module, it multiplies the time it will take to complete the attack on the structure.
To determine the defense multiplier bonus for a system, find the current value (see table above) of the system indices level in each of the three indices and add them together, then add 1. If the final result is above 6, cap it at 6. The 'Attributes' tab of structures affected by the Entosis Link module will show a 'Base Capture Time'. Multiply this time by the multiplier gained with the system indices and that is the amount of time it will take to fully attack the structure.
The Capital System of an alliance will receive a +2 bonus on its Activity Defense Multiplier. However, this bonus will not increase the Multiplier beyond 6x.
Further information about the Defense Multiplier can be found in the Summer 2015 Nullsec and Sov Status Report developer blog.