If that's what they spliced it with, it was wired for phone and probably won't work for ethernet. It's possible to run 10Mbps ethernet over ancient cat3 wiring, but it still needs to be connected properly. If all four outlets meet in one spot, they can just be wired together for phone but would need a switch for ethernet. And you typically don't want to have the switch up in the attic.
If feasible, I'd rip it out and replace with modern stuff (Cat6a or thereabouts), routing all the outlets to somewhere a switch can reasonably be located. If the wiring is cat 5 or better it would probably work if you replaced any such joints with a proper "network" one (may not do gigabit, but probably 100Mbit), but it would still be kinda iffy.
If that's what they spliced it with, it was wired for phone and probably won't work for ethernet. It's possible to run 10Mbps ethernet over ancient cat3 wiring, but it still needs to be connected properly. If all four outlets meet in one spot, they can just be wired together for phone but would need a switch for ethernet. And you typically don't want to have the switch up in the attic.
If feasible, I'd rip it out and replace with modern stuff (Cat6a or thereabouts), routing all the outlets to somewhere a switch can reasonably be located. If the wiring is cat 5 or better it would probably work if you replaced any such joints with a proper "network" one (may not do gigabit, but probably 100Mbit), but it would still be kinda iffy.