Once a year, software engineer Manish Mattawar makes a pilgrimage to his hometown Nagpur to spend a weekend sitting still in front of a laptop.

“I cannot move until I finish and I can’t afford to," he says. “I remember starting at 10am and going on till at least 4am next day—until I almost slept on the keyboard."

Mattawar is frank about calling this odd annual ritual “an addiction", but he’s not alone. Nearly 80,000 people around the world spend a weekend in November staring at a computer screen—attempting to be the first 250 to solve the fiendish puzzles that form part of Klueless, Indian Institute of Management (IIM), Indore’s annual online riddle game.

Clued in: The ‘Kluemasters’ of the upcoming Klueless 6. The team designs the puzzles and monitors the game 24x7 once it goes live. Shankar Mourya/Mint

Here’s an example. Your browser is pointing to a white page with an answer bar on top. The title of the page says “Follow the middle path", and the URL of the page ends with “cleopatra.asp". Hidden in the source code is a line in Italian, italicized, that translates to “taken to the doctor, after a snakebite". Simple solution—change the URL to “cleopatra.doc" (“asp" is an archaic word for snake) and you get a Word document that forms the second part of the puzzle.

This was part of level 24 of last year’s Klueless (the fifth iteration of the game), one which prompted a player to email the creators—“WOW! WOW! WOW! The sheer brilliance of this level took my breath away. Whoever created this, will you marry me?"

Now in its sixth year, Klueless has become a vital part of the build-up to the college’s annual festival—Ahvan. The Klueless site sees nearly three million hits from 108 countries while it’s running, and a live blog that generates five comments a minute from vexed players. The structure of the game is based on NotPr0n (http://www.notpron.com)—an online puzzle site launched in 2004, months before the first Klueless.

“It’s a simple idea—players use logical reasoning to cross “levels" which consist of simple pages on the Internet," says event head Akarshan Gupta. “Common techniques include changing the URL to get ahead, or hiding hints in a page’s source code." Gupta makes it sound simple, but Klueless puzzles are exercises in lateral thinking. Players are often encouraged to read up on topics such as cryptography, and it’s not uncommon to agonize for over 12 hours on a single level. “It introduces you to things you never knew," says Mattawar. “I learnt to decode bar codes to solve a level in K3, and I remember going—cool, now I can read bar codes!"

Most Klueless players are working professionals, which is why the game usually goes live on a Thursday—giving office people a weekend to finish (two days is the expected par time). A countdown appears on the main site a few days prior to the start of the event, one that’s watched with much excitement by regular players. Cheating is actively encouraged, as “any means whatsoever" can be employed to solve a level. The Klueless team (currently eight people) monitors the game 24x7, disbursing cryptic clues if players seem stuck. The blog and forum serve two important purposes—you can find out how far players have got (if, like Mattawar, you wish to make the elusive “hall of fame"), and it’s a social hub for the players, who discuss hints and possible solutions.

The forums are also a fascinating barometer of how well the puzzles are designed. Common laments from players range from the determined—“If I don’t crack this in 24 hours, I’m legally changing my name to the answer of this puzzle"—to the bizarre—“Please, please give me a hint. I will post a video of myself dancing naked if you give me a hint."

“Right from the beginning, the challenge has been to make it tough enough to engage, but not to an extent where it puts off people," says Amit Sharma, who designed the first Klueless. It started, he says, as something to fill up available space on the site servers. “But it went viral thanks to posts on forums like PaGaLGuY.com and Team-BHP.com," he says. “They all said—‘if you want to crack the Common Admission Test (CAT), try this!’ In India, that’s a guaranteed bringer of heavy traffic."

Four hundred people completed the first Klueless, with top honours going to Paromita Deb Areng, a student of IIM Kozhikode. The winners change every year, and come from around the world. “Four of the top 10 in 2009 were from US universities," says Gupta. Mattawar, who has come seventh two years in a row, is the closest the game has to a star player. “It’s not a joke to be on one of these websites forever," he says. “It’s like getting your name in the newspaper and not for something illegal."

What keeps him coming back is the sheer thrill of participating in a live, global race to the finish. “I can never forget the moment when you crack the last level," he says. “It’s just like the last lap of the Jo Jeeta Wohi Sikandar race. When Aamir Khan crosses the line before his rival—there’s satisfaction, pride and joy. All in one."

Klueless 6 starts on 18 November. For more information, log on towww.facebook.com/Klueless6