"This is a historic act of devastating incompetence, to have created such an arsenal and then stored it all in one place," Assange said.
"It is impossible to keep effective control of cyber weapons... If you build them, eventually you will lose them," Assange said.
Assange was speaking in a press conference streamed live from Ecuador's embassy in London, where he has been living as a fugitive from justice since 2012.
He said his anti-secrecy website had "a lot more information" about the Central Intelligence Agency's hacking operation but would hold off on publishing it until WikiLeaks had spoken to tech manufacturers.
"We have decided to work with them to give them some exclusive access to the additional technical details we have so fixes can be developed and then pushed out.
"Once this material is effectively disarmed by us we will publish additional details about what has been occurring," he added.
WATCH: WikiLeaks reveals CIA hacking tools
CIA questions Assange 'integrity'
On Tuesday, WikiLeaks published nearly 9,000 documents it said were part of a huge trove leaked from the CIA, describing it as the largest ever publication of secret intelligence materials.
"This extraordinary collection, which amounts to more than several hundred million lines of code, gives its possessor the entire hacking capacity of the CIA," it said.
In Washington, the CIA, hit hard by the apparent leak of much of its cyber-spying arsenal, defended itself while criticizing the WikiLeaks founder.
"As we've said previously, Julian Assange is not exactly a bastion of truth and integrity," said spokeswoman Heather Fritz Horniak.
"Despite the efforts of Assange and his ilk, CIA continues to aggressively collect foreign intelligence overseas to protect America from terrorists, hostile nation states and other adversaries."
Assange: CIA was 'careless'
The documents showed that CIA hackers can turn a TV into a listening device, bypass popular encryption apps, and possibly control one's car.
Most experts believe the materials to be genuine, and US media said Wednesday that the Federal Bureau of Investigation is opening a criminal probe into the leak.
The investigation could focus on whether the CIA was sloppy in its controls, or, as The Washington Post reported, it could be "a major mole hunt" for a malicious leaker or turncoat inside the agency.
WikiLeaks itself said the documents, hacking tools and code came from an archive that had circulated among US government hackers and private contractors.
"The CIA has been so careless to produce this material. So do various cyber mafia already have it? Do foreign intelligence agencies already have it? It's quite possible numerous people already might have it," Assange said.
WikiLeaks has stunned the US government with a series of publications of top secret political, diplomatic and intelligence materials in recent years.
The CIA on Wednesday accused the group of endangering Americans, helping US rivals and hampering the fight against terror threats through its leaks.
"The American public should be deeply troubled by any WikiLeaks disclosure designed to damage the intelligence community's ability to protect America against terrorists and other adversaries."
"Such disclosures not only jeopardise US personnel and operations, but also equip our adversaries with tools and information to do us harm," Horniak said.
While refusing to confirm the authenticity of the documents WikiLeaks published, Horniak stressed that hacking is a normal part of its mission "to be innovative, cutting-edge, and the first line of defence in protecting this country from enemies abroad."
WATCH: Technology analyst Trevor Long explains impact of WikiLeaks claim
