I keep getting hacked…

Ok, so i keep getting hacked, i think.

It first happened on the 8th of August, and i thought id solved it.

What keeps happening is iframes keep getting put into files, not any files though –

default filters.
default widgets.
index pages.
( these are ones with wordpress )

( these are cutenews files )
index
skins
data

i tried making all files 644 permissions, but it still hasnt stopped. i removed all the iframes i find and then i upgrade my wordpress if there is an upgrade. i even thought it was because i was logged into my ftp programme, but i didnt go on at all yesterday to see if this was the problem, but when i woke up this morning its happened again. its really annoying me, almost upsetting me really. i just really want some help on how this is happening, why it is happening and how i can stop it. please. oh, and i might add, the only sites i host seeming to get these iframes are ones who use wordpress or cutenews or the coppermine gallery. because its only these files getting the insertion.