Mods can increase the effects of a portal. There are six types of Mods:

Shield – Increase the defense of your portal and resonators surrounding it making it harder to take down by enemies.

Link Amp – Increase the portal’s potential link range. A rare Link Amp will effectively double the portal’s link range.

Heat Sink – Reduce the cooldown time between portal hacks.

Multi-hack – Increase hacking capacity of a portal before it goes into the burnout mode. Normally, portals could be hacked up to four times within a four hour period.

Force Amp – Increase damage dealt to attackers or enemies trying to hack the portal.

Turret – Increase the frequency of portal attacks against enemy agents.