When the Ministry of Defence first came across Wikileaks, staffers were stunned. "There are thousands of things on here, I literally mean thousands," one of them wrote in an internal email in November 2008. "Everything I clicked on to do with MoD was restricted... it is huge." The website, an online clearing house for documents whose authors would generally prefer them to stay in the private domain, has since been banned from the MoD's internal computers, but it did no good: eventually, that email ended up on Wikileaks. And when a US Army counter-intelligence officer recommended that whistleblowers who leaked to the site be fired, that report ended up on Wikileaks too.

The authorities were right to be worried. If any further proof were needed of the website's extraordinary record in holding the authorities to account, it came this week, in the release of shocking video footage of a gung-ho US helicopter attack in Iraq that killed 12 people, including two unarmed employees of the Reuters news agency.

The US government had resisted Freedom of Information requests from Reuters for years. But when an anonymous whistleblower passed the video on to Wikileaks, all that quickly became futile. An edited version of the tape had received almost 4 million hits on YouTube by last night, and it led news bulletins around the world.

"This might be the story that makes Wikileaks blow up," said Sree Sreenivasan, a digital media professor at New York's Columbia Journalism School. "It's not some huge document with lots of fine print – you can just watch it and you get what it's about immediately. It's a whole new world of how stories get out."

And yet despite Wikileaks' commitment to the freedom of information, there is something curiously shadowy about the organisation itself. Founded, as the group's spokesman Daniel Schmitt (whose surname is a pseudonym) put it, with the intention of becoming "the intelligence agency of the people", the site's operators and volunteers – five full-timers, and another 1,000 on call – are almost all anonymous. Ironically, the only way the group's donors are publicly known is through a leak on Wikileaks itself. The organisation's most prominent figure is Julian Assange, an Australian hacker and journalist who co-founded the site back in 2006. While Assange and his cohorts' intentions are plainly laudable – to "allow whistleblowers and journalists who have been censored to get material out to the public", as he told the BBC earlier this year – some ask who watches the watchmen. "People have to be very careful dealing with this information," says Professor Sreenivasan. "It's part of the culture now, it's out there, but you still need context, you still need analysis, you still need background."

Against all of that criticism, Wikileaks can set a record that carries, as Abu Dhabi's The National put it, "more scoops in its short life than The Washington Post has in the past 30 years". By earning its place as the natural destination for anyone with sensitive information to leak who does not know and trust a particular journalist – so far, despite numerous court actions, not a single source has been outed – Wikileaks has built up a remarkable record.

Yes, it has published an early draft of the script for Indiana Jones and the Kingdom of the Crystal Skull, and Wesley Snipes' tax returns; but it has also published the "Climategate" emails, an internal Trafigura report on toxic dumping in Ivory Coast, and the standard operating procedures for Guantanamo Bay.

Whatever the gaps in its procedures, there is little doubt that the website is at the forefront of a new information era in which the powerful, corrupt and murderous will have to feel a little more nervous about their behaviour. "There are reasons I do it that have to do with wanting to reform civilisation," Assange said in an interview with salon.com last month. "Of course, there's a personal psychology to it, that I enjoy crushing bastards. I like a good challenge."

Full disclosure: What we wouldn't know without Wikileaks

Trafigura's super-injunction

When commodities giant Trafigura used a super-injunction to suppress the release of an internal report on toxic dumping in the Ivory Coast in newspapers, it quickly appeared on Wikileaks instead. Accepting that the release made suppression futile, Trafigura lifted the injunction.

The CRU's 'Climategate' leak

Emails leaked on the site showed that scientists at the UK's Climate Research Unit, including director Phil Jones, withheld information from sceptics

The BNP membership list

After the site published the BNP's secret membership list in November 2008, newspapers found teachers, priests and police officers among them. Another list was leaked last year. The police has since barred officers from membership.

Sarah Palin's emails