my 3 possibilities

1. clones of themselves

2. Sharks *ones with freakin laser beams attached to their heads*

3. sea bass

rofl

Okay since were joking about I think

zippy bungle and george

And all , planets lost the tune can be heard
Sings....
"Up above the streets and houses, rainbow flying high! Everyone can see it smiling RAAAINBOW .........etc"

Must be there uber broadcast centres putting out the death tune ^^

Fools, it's so obvious.
They tried to make a Fallout sequel, turned it into a FPS, and the NMA mob found out.
The massive flaming on the internet boards created a raging supertroll, now devouring the galaxy.

You can just tell that they were ANDROIDS, end of.

Look, their crazy creator sent out spybots into the Vasari, TEC and Advent empires and took samples of their cells and took photo shots of their orbital structures and samples of nano bla bla bla. For years he created the ultimate fleet which looked just like the people from these factions. And gradually he sends out them droids to exterminate the 3 factions. He obviously went for Vasari because they are an ugly and horrid species, then he's gonna go for TEC because that was he previous homeworld, they threw him out because they did'nt believe that war and conflict would overcome their world. And then Advent, becuase hmmm its the last of the 3 factions.

or following the storyline:

the crazy creator sent out spybots into the vasari empire, replicated their ugly mugs, copied their structures and technology and made the same ships. Everyone looks like a Vasari thing but this is where it all started 'FROM WITHIN THE EMPIRE'

cool, eh?

that would bite those kill everything

I don't really think the nanobot theory makes much sense, because the Vasari are being chased. Last time I checked nanobots weren't really built for long-distance travel.

The Vasari also don't know what has been chasing them, so they obviously can't "learn their lesson" because they don't know anything about whats chasing them.

One more point against the nanobot theory is that if a heavily damaged ship came back it would be rapidly falling apart- that's what nanobots do, deconstruct things.

I don't really think that an inorganic explanation will be the right one, mainly because they would never program something to slaughter them and pursue them thousands of light years through space. And if they had the level of technology to program sentient androids it would be specifically stated in the lore.

That leaves us with another race/a race they created is trying to kill them. I think either of these would work as an explanation. But I'm leaning towards a new race, not a Vasari slave race. Mostly because they say that they harshly assimilated any races advanced enough to pursue them as fast as they could flee. Its strange because the manual seems to both hint at and hint against the slave race uprising scenario.

The most probable pursuers are bio experiments, mainly because of the lab shown in the opening sequence, but, if they were an incredibly strong intelligent adaptable race, then they could probably accomplish as much as my final possible scenario.

Despite this, I think that there is another, more advanced race pursuing the Vasari and forging an incredibly vast empire with the technology to destroy the entire dark fleet before they can even give the order to retreat.

Actually It's a race thats basicly way more powerful than the vasari. There will be an expansion coming out for Sins and this new race will be playable along with a few other new races. Also a campaign. I'm not sure what kinda of Alien Race is chasing the vasari but there pretty powerful. I think this information was leaked on some sites.

you guys have to remember that it is something the Vasari created. if u guys were paying attention.

The most evil entity the universe has ever seen - RIAA

Jack Thompson. He's gotta be ticked.

Top 10 theories of things or people chasing the Vasari

10. William Shattner's old toupee
9. The Orange dude who "Hankered for a hunk of Cheese" from the old Schoolhouse Rock cartoons. (It's a Wagon wheel!)
8. An Inconvienient Truth.
7. A Carlos Mencia sketch gone wrong.
6. The result of Bill Clinton not inhaling.
5. Angry race of aliens striking back at high gas prices.
4. Unknown race trying to expand their cell phone coverage but inadvertently destroying everything in their path (Can you hear me now?).
3. Contestants on the intergalactic reality TV show "Who Wants to Be a Harbiger of Doom?".
2. Paris Hilton's delision of being talented and important taking physical form.

And the #1 Theory of things or people chasing the Vasari...

You guessed it: Frank Stallone.

The Vasari created Halo 3, and distributed it throughout their planets. Everyone played it at the same time, and the shockwave that was created from every single one of their race screaming NOOB at eachother destroyed everything and is now travelling through space in super-sonic speeds, leaving nothing alive.

They would have created it, so it supports that theory.

Then it would not be another race but an unstoppable wall of brain-melting sound.