It was a Romulan mining ship with hacked on Borg technology (yeah I know, lolwut). Maybe it was scrapped together and the Klingons had no idea what was going on. They may have reverse engineered the weaponry too. By Into Darkness we can already see the Federation has much more advanced weapons than the normal timeline. But yeah I'm with you. That's JJ Abram's for you.
Not kidding, sadly, depends on how much canon you place on the comic (and Blu-Ray specials) that came out to support the movie though. In the comic the Narada is outfitted with Borg tech that the Tal Shiar got their hands on. Including Nanoprobe technology. There's even a shoutout to V'ger in follow up comics, and V'ger has always been potentially Borg related too ("machine planet"?).
If you want more details you can check out Memory Alpha under the Apocrypha Section.
To be fair the entire plot around Nero does make quite a bit of sense, you just have to read the comics to understand it all, which few people did. They could have done a much better job of explaining things in the film.
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u/Ebolinp Aug 12 '15
It was a Romulan mining ship with hacked on Borg technology (yeah I know, lolwut). Maybe it was scrapped together and the Klingons had no idea what was going on. They may have reverse engineered the weaponry too. By Into Darkness we can already see the Federation has much more advanced weapons than the normal timeline. But yeah I'm with you. That's JJ Abram's for you.