Mystery//01 Mia and Grunty
When the player trades with Noble and Iron Grunties, the number of trades with Mia increases in the "Ryu Books."
NOTE: this mystery further hints the fact that Mia is an AI, which is why when you trade with the grunties (which are also AI) her trades go up.
Mystery//02 Sieg
The character, Sieg, played by Tomonari Kasumi appeared as in the game. He is one of the two players talking about Mia at the Chaos Gate in Mac Anu. Though the incident in the game and the OVA follow the same timeline, it seems as though Orca fell into a coma before Tomonari did.
Mystery//03 Six Players in Coma
In ".hack//Liminality in the case of Mai Minase," Tokuoka says that there are six players who fell into a coma like Tomonari. From the accounts of the game: Tomonari Kasumi, Orca, Alf, and an individual related to BlackRose can be confirmed. At this time it cannot be confirmed wheter "Tsukasa" from ".hack//SIGN" and others from the real world are included.
Mystery//04 Chat
There are two ways players can communicate in “The World�. The first one is “Open Chat,� which allows multiple players to congregate and communicate with everyone. The other is “Personal Chat� where the conversation is one-on-one. By using “The World Makeup Language System (WMLS)� developed by CC Corporation, it is said that there is no difficulty in selecting either format of chat function.
Mystery//05 The World Version Updates
“The World� has been upgraded numerous times, and with each version upgrade several functions have been added or limited. The fact that Plyer Killing (PK) that was possible in .hack//SIGN has now been disallowed in the game shows that there has been a major upgrade in the system. The official version announced by CC Corporation are the following:
2006 Fragment ver. alpha-01
2007 Fragment ver. beta-02
2007(end) The World ver. 1.00
2008 The World ver. 1.40
2009 The World ver. 1.81(.hack//SIGN?)
2010 The World ver. 2.01(game & OVA)
NOTE: I guess that's the reason I can't kill Mistral when she starts shrieking.
Mystery//06 The Red Chaos Gate
A red Chaos Gate appeared in front of BT and Crim at "Hidden Forbidden Holy Ground" in .hack//SIGN. The field of "Hidden Forbidden Holy Ground" was first constructed as a Root Town by CC Corporation, but was discarded for some reason. It is said that Helba created an original Chaos Gate using that discarded field. Because of this rumor, the red Chaos Gateis known as the "Helba Gate," but the field that is connected from the "Helba Gate" was not created by Helba. Of course, these are only rumors...
NOTE: This bit of info combined with what we know thanx to Bear from SIGN and what Albireo says in AI Buster, givesalot of insight into why that field is so unique.
Mystery//07 Engraving on the Sword
In the "Log In" screen of "The World" there is a sword with an engraving of "Key of the Twilight." Apparantly, the incident which took place in .hack//SIGN was also a major prolem for the CC Corporation. A massive personnel change was also conducted within the company. Since then, CC Corporation and the succeeding System Administrator have decided to gauge the reactions of users regarding this mysterious item, "Key of the Twilight."
NOTE: Guess that's why the sword is engraved like that (*_*;) I bet that's this is the work of that pig-headed Lios.
Mystery//08 Data Drain
In the game, Skeith performs Data Drain on Orca, and Yasuhiko, Orca's real world counterpart, falls into a coma. However, in the battle with Skeith at the end of ".hack//INFECTION" the party members do not fall into comas when Skeith performs Data Drain. The power of the bracelet seems to lessen the force of Skeith's attack... but if Skeith had performed "PROTECT BREAK" on the party, the outcome could have been different.
NOTE: *imagines BlackRose falling into a coma after being DD'd* NOOOOOO!!!!!!!
Mystery//09 Piros
Based on the way Piros looks and by his actions, he is obviously not a regular player. In reality he is a 31 year old married graphic designer who works for CC Corporation and plays "The World" both during and after work. He edited his character in secret.
NOTE: That's certainly... interesting, I guess I have a spy on my team *kicks Piros out of the dot-hackers team*
Helba tried to have a conversation with Balmung, and so Helba would not mess with him, Balmung said "I do not speak with hackers" as kind of a final statment. (Helba has a way with words) 
