Is the 7% added so if i had 60% it would be 67%, or does it add 7% if my attack.

7% to your attack.

i did the math a while back... if i'm remembering correctly, for a conservative value you can simply do 60% * 1.07 = 64.2%
that would be the very minimum amount the unit will increase it to...

...though in actuality, the lower your regular attack the larger the gain you'll notice....

Your normal invasion chance is INV.ATT/(INV.DEF*3). If say you add in an atmospheric decimator, your new chance is (INV.ATT+100)*1.07/(INV.DEF*3). Given a moderate invasion attack of say 4000, your new chance will be about 10% higher than without the decimator.

Lycan's formula of multiplying by 1.07 is if you have a _lot_ of invasion attack... which is often not the case. You notice the decimator more with less INV.ATT since it adds its own 100 invasion attack along with the 1.07 multiplier

For reference:
INV.ATT is all attack and invasion attack you have
INV.DEF is all attack and defense and invasion defense on the planet you are invading

....that's what i said...