Ultra strikes are a new type of weapon released with the moto-droid phone line put out by motorola. Unlike the normal bursters which disperse in a wide range arcing further out (dependant upon level), These bursters are concentrated to a tiny area. (you have to be standing on the resonator or the portal or you will miss)
These new bursters which are publicly hackable now (originally only available to be hacked by agents with the droid-x phones) are useful for knocking mods off of portals without hitting the resonators or for taking out single resonators at a time.
Like it’s xmp brother, ultrastrikes come in levels 1-8 and have hack similarly to power cubes, where it will release a ultrastrike that matches the level of the portal.
Ultrastrikes have a similar breakdown when it comes to recycling them for xm, as regular bursters do. Which gives you 20x the level of the ultrastrike in xm.