I got a question that I don't want to find out by experimenting and I couldn't find anything on this forum and the wiki wasn't clear either.
If I successfully perform a covert op, will my victim know that I am responsible? Can he find out?

You can see why I wouldn't what to find out by testing, eh?

as far as i know he wouldn't know you.. but if your spy was caught during your attack..be prepared he might get back to you

Thanks. Out of curiousity, how much days of spy protection does an experienced user have? Hundreds? Thousands?

All personal preference, some call it a waste of energy, some just add a little every time they have a little excess energy, most leave their spy on their colony for the duration of the era - giving them a lot of protection. Only one way to find out I guess!

That's actually an interesting point: When I had just stated playing, I thought I read something about spys giving protection, and there is also a "Spy Battle" tooltip.
But when I tried to look it up again, I couldn't find it anymore, so I began so suspect that it's not actually true.
I guess that means that each "infiltration point" my spy has in my own colony counts as one point of spy protection? That'll make it hard to ever infiltrate a colony that has kept its spy at home from the start. Which I haven't, now.

I guess that pretty much puts all my espionage plans on hold.

Last time I checked, that is correct.

(Keep in mind I'm just coming back from a six month break, don't count on that being up-to date)

yes that is absolutely right.. each infiltration of your spy in your colony/castle is a point for spy protection..

so i suggest you try to recruit a spy as early as possible in the game..

additional adv*: if you have a spy, it will only costs you 20 energy/mana to put up a 50 ticks spy protection instead of the usual 50 energy/mana if you don't have.

here's a quick scenario for you about spy battle:

scene 1: you have a spy with 70 infiltration in your colony.
scene 2: an enemy spy with 20 infiltration in your colony.
scene 3: the enemy spy try to perform operation.

result: you will be able to kill the enemy spy as you have more infiltration, and it will show the owner of the spy, your turn to make him pay!

hope this helps you!

Just going to add for your convince -

('y' must be less than 'x')

If you have 'x' ticks of protection on your colony and a spy attacks with 'y' amount of ticks, 'y' ticks will be deducted from 'x'

Eg.

Attack with 92 ticks of infiltration

Defender has 189 ticks

Attacker loses spy

Defender loses 92 ticks of infiltration from their colony/outpost etc leaving them with 97 ticks of spy defence.