Alt is short for alternate account. Alts can be used for trolling/insulting (MatterSparky by Mizuki, AnalBeads by Orcaguy), as a joke (100lel by _cookieFONSTER_) or simply for the purpose of having another account.
As admins can see IP addresses, they can use this to determine if one user is an alt of another. They can use this if they suspect if someone is trolling with alts.
One of the most well-known alts is Sleipnir. Sleipnir is an alt by ChaoticNeutral, and used it to attack others. Chaotic later got a permaban, along with Sleipnir and fluttersisbest. ChoticNeutral returned as Chaotic_Neutral.
Kitten_Masters = MasterSparky
lolasdfwqerty, CanStopButtnugget2 = 1234abcdcba4321
cookiefonster2, awesomeguy123, Master_Sparky, 100lel, 9876zyxwxyz6789 = _cookieFONSTER_
InfinityFingers, CC_Sucks^+, CCisBoring, everyone^, 200rofl^ = BurntCookie
Donkey_Kong, BurthCookie = TFU_Satron
I00lol+ = john4s13
AnalBeads+ = Orcaguy
RebeccaBlack+, Oralpaeb+, __ButtNuggetGod__, ButtNuggetWarrior, IHM_RETURNS_5TH_TIME+, achoo+, whoawhat+, Atrocious_Monstrocity+ = I_HATE_MISDEER
Optipai, TFU_Zatron, 10olol = IdleGamesRock
^ = email not confirmed
+ = deleted
Unknown: Tellerium, KhantStopButtnugget, 1OOlol, Blissful_Secrecy
Alt theories Edit
(post by BurntCookie)
1. ClickingGhost once said he spammed the inbox of 100lol (source). What did cookiestealer do? Spam the inbox of 100lol with hardcore gay nazi porn. He probably didn't mention grisha and Idler because the post he replied to was about 100lol, and not grisha or idler. CG made that post just one day before Idler said his inbox was spammed, along with 100lol's. Of course, it's still possible that cookiestealer is separate from CG.
2. ClickingGhost has a similar avatar to what cookiestealer had, if I recall correctly. (both related to hacking)
3. cookiestealer spammed the inboxes of some people: 100lol, possibly grisha5, and Idler. Who was on CG's hate list at that time? That's right: 100lol, grisha5 and Idler. CG hating others could give him an incentive to spam the inboxes of those users, and as he didn't want his main account banned for spamming inboxes, he created an alt to spam those accounts.
CCisBoring = BurntCookie (proven correct) Edit
(post by RedCookie666)
1. One of BurntCookie's older avatars (unstable antimatter condenser) is the same as one of Zagorakis' (someone on another forum) older avatars, and one of CCisBoring's older avatars (MOAB-class bloons on Space Truckin') is the same as another one of Zagorakis' older avatars.
2. CCisBoring mentioned in what I believe is a deleted comment on his own wall that he prefers Ninja Kiwi. Where is Zagorakis? The Ninja Kiwi forums. Where are Space Truckin' and MOAB-class bloons from? Bloons Tower Defense 5. Who made BTD5? Ninja Kiwi. Who owns the Ninja Kiwi forums? Ninja Kiwi.
3. On page 1591 of a thread (I love/hate it) on the NK forums, Zagorakis asks the next user if he loves or hates if Cookie Clicker and all traces of it were removed from the Internet. Another user (whose username will be kept secret) said that he would love it. In a deleted writing on someone's wall, he posted a picture. What was the picture? The previously mentioned scenario, minus the usernames, dates and icons.
4. In one if CCisBoring's comments, he said if Justin Bieber penis worship became a national holiday. This reminds me of a post Zagorakis made where he said if Ninja Kiwi became a national holiday.
5. In another one of Zagorakis' comments, he says this:
"Cookie Clickers. (It's a poor ripoff of an already boring game! What's more, lots of people at school play it!)"
The word I bolded is boring. What word does CCisBoring have in his name? Boring.
6. CCisBoring's last writing on his wall is that he is a test to see how people would react if an actual Cookie Clicker hater appeared.
grisha5 = 100lol Edit
1. Grisha and 100lol have similar grammar
2. Grisha and 100lol both had kitten avatars.
3. Grisha and 100lol both hate ThatDude.
grisha5 =/= 100lol Edit
1. grisha5 is Russian. 100lol is Lithuanian, apparently.
2. grisha5 and 100lol have been seen to be both active simultaneously.
3. There are slight grammar differences "xD" and "XD"
4. grisha hates "pussy" and FASTER MENNER!!!! 100lol likes these things.
5. 100lol claims to have impossible amount of cookies and wall damage. grisha thinks this is impossible.