I've seen this thread before, but haven't read this:

It only just dawned on me as I've three chars at varying levels who all just completed the "rescue Thorald from the Thalmor" quest. All three got their first assasin's attempts/notes immediately after this quest. Coupled with the non-DB Khajit in Riften, it seems that these anonymous malefactors are most likely the Thalmor. If this has already been a reached consensus, sorry.

Not really. This is a completely random encounter; none of my characters ever rescued Thorald, but they were attacked by DB. Thalmor seems to make sense, but it happened to my non-Dovahkiin character too. It's just random.

Never played any DB quests in either Oblivion or Skyrim, so I still don't know much about them... But don't the Thalmor really hate the DB and try to wipe them out?

I had a Khajit come up to me at night right after Helgen as I was making my way to Riften. So no its not linked with the Thalmor prison or embasy. I was level 10 at the time of the attack and was only a few hours in. Not even been to Whiterun at the time either well ok I was there but the guards chased me away as I got caught pickpocketing a stable hand.

The Thalmor has a grudge against anything and anyone it can't control + the Dark Brotherhood are not worshipping the eight divines.

Not only have I had to deal with a couple of DB assassins as the OP describes but just recently I walked into Winterhold and was assaulted by 4 thugs that followed me into the Frozen Hearth Inn. As they attacked me the mage that lives at the Inn,Nelacar I believe,jumped into the frey and let loose some bada** lightning attacks that soon had the thugs crispy fried on the floor.After searching them I found a note from the person that hired these guys to put a beating on me,It was a NPC named Grelka,a Nord woman in Riften that I had never had any contact with ....ever.I couldn't figure the reasoning behind that attack. They may be just random events.....

Two of my main characters have done Missing In Action, the third hasn't even initiated dialogue with Fralia about Thorald. All have had assassins sent after them.

Yes, R. Dom N'Countre` sends them.

I've never gotten any on either of my characters, but I Fast Travel almost all the time. Plus, on my Warrior Dude I destroyed them and my Assassin Chick joined them pretty early on.

100% random. I've gotten dork brother attacks as early as level 5 on some characters. As by that time I was just leaving riverwood for the first time there can be no other explination. The "hired thug" attacks are also random.

Ditto, DB has been confirmed to have no other level requirement then level 5.

No they arent the thugs carry a note as to who hired them. The thugs can be triggered for crimes where you werent caught.

One player also got thugs sent after him from

You can even get thugs hired by dead people!!

Okay, okay, I admit it. It was me, bacause I had to be the one and only dragonborn in Tamriel.

On characters who haven't commited any.

I *think* that may just be something the player's missed. I've never gotten a thug note that wasn't because of something I did directly. Actually, Grelka's quite a busy one. How many times have you clicked at the wrong moment and "stolen" that armor? C'mon, not even once? And, the thing is, at low level, with everything going on in the market, likely Brynhjolf also getting in your face, Grelka often lets it slide, but she'll say something like, "I saw you take that" as Brynhjolf breaks into his spiel. I don't routinely look at my PCs' stats. Actually, I don't look at them at all. But, I guess it would be nice if there was a "grudges" listing to at least let you know it wasn't random.

In that respect, did y'all know there's a Romeo-Juliet thing going on with the Battle-Borns and Grey-Manes? Just found that out tonight. I'd killed Jon and found "Olfhild's Note" on his body. Criminy, just when I thought I was down to one last old coot, there's a pre-Battle-Born lady in waiting that's now gonna hire some thugs to die on my blade.

It was Braith!

I wasted the DB at a low level...have never had a DB attack on this character.

Had the hired thugs jump me after I accidentally clicked on a 1 gp cup at the new gnisis corner club and had the owner's name on the note. (made over 1000 gp on the thugs, roleplayed that he sent the thugs to me to conveniently eliminate...all were nords so I my dark elf had no qualms about killing them)

Had the Thalmor send justicars after me only after I wasted a thalmor patrol in front of their embassy...Why yes I do worship Talos...whatch gonna do about it goldenrod?????

Thats all this character has had in 33 levels...I feel cheated somehow...what am I...chopped liver?

Waah! No one cares enough to send killers after me!

The first thug trio I ran acrost in my current game was hired by someone I hadn't even spoken to. In a hold I didn't travel to for another month.

Moira?

Happens if you kill Anise. Guess they're best buddies.

I kiiled Anise after I wasted the DB...never got an attack then or since.

Word does spread. While bounties don't carry hold to hold, personal grudges do carry-over and you can be targetted by someone from another hold if you do something to someone they know in another hold.

I know the old braod is still alive. So clearly it had nothing to do with that. It was some dude from Markarth who selt the thugs. Don't recall who.

Then maybe you can't recall what did either or your confusing the names of a marakath resident with a riverwood one say Orgnar and Odvan.

Or accidently steal a book from her, after some bandits killed her.

They are sisters, actually. I had to look it up since I had no idea who Moira was and what I had done.

Actually they are hired by Mavin Black-Briar: go down to her basemant and you'll find the Black Sacrament gear and a letter to the DB complaining that they haven't managed to whack you yet. This is true even if you are in the TG and have already done the job for her. I'm not sure what happens if you go to her basemant before the DB first attacks you, but I would guess the stuff is still there.