A reckless government agent learns his long lost brother is a test subject of a government experiment, leading him to team with terrorists to mount a rescue.

I agree with Blajay very much - having the protag move out of his usual space provides conflict (if he is already 'reckless' then teaming up with terrorists aint a big move). Also, thinking about the 'terrorists' to make them a bit more redeemable, overtime, thus justifying (possibly) the teaming up with them, could be a useful way to go - so that the audience perhaps the question is raised - who are the real terrorists - the rebels or the govt doing experiments on the guys brother?

So building on Blajays, how about:
"When a well decorated federal agent learns his long lost brother is a test subject of a government experiment, his only hope is to team with 'cyber terrorists' to mount a rescue.?

I would think something along the lines of
"When a well decorated federal agent learns his long lost brother is a test subject of a government experiment his only hope is to team with terrorists to mount a rescue."
provides conflict and obviously creates an immediate room for character arc

Hi bro,

I would try to find a substitute for government as that word is strong like hell and it resonates in my head whenever I read your logline aloud (may be my own subjective feeling). If you say military experiment, I think that military connects in people brains.

Its also better to start with When, If, While, As ....

"Leading him" is passive too. And the whole second sentence just feel no good, there would be a plenty other options to alter it.

Reckless is also a negative perk. But that's ok when you mention the path your hero has to go, like he has to (internal change) to be able to safe him.

Like:
When a reckless government agent learns that his long lost brother is a test subject in a military experiment, he join terrorists and leads an attack for his rescue.