Security services installing a virus on a laptop on the move? Really?

I was listening to a radio play the other day about GCHQ. A team of three were tracking three suspected jihadis from Cardiff who were on their way to Syria. These three had (I think, I couldn’t quite make it out) a ‘satellite wifi modem’ or something which, apparently GCHQ could hack into in real time and instal a virus. While doing so they discovered that Assad’s cyner bods had done the same and were planning a drone attack on the three because they could follow their progress.
Is any of this possible? Can GCHQ/Assad really remotely install viruses in the laptop of someone on the move?