I will try to find the article that supports this line of thought, but Christians converting to Islam in the Philippines do not stand out from the crowd, especially if they are taught to keep a low profile. When they return to their homes, let's say somewhere in Luzon, they speak the local dialect, they wear the same clothes, they are probably well known in their community, and there is absolutely nothing abnormal about a Filippino or Filippina going to work in the Middle East. They provide at the very least an auxillary and probably an underground to help facilitate terrorists. Lets assume they also have been contacts and clandestine ways of communicating with them.

Balik Islam is a threat, and beyond the physical threat it is interesting to note the large number of Filippionos who travel to the Middle East that convert from Catholicism to Islam. I read a couple of years back that this was happening in Mexico also, largely because the Catholic church didn't offer any explanations as to why they (the majority) are suffering in abject poverty, or offer a way ahead like the promise of Islam provides (so I'm told). This is perhaps the real threat long term, Western society is gradually being undermined.