Software firm Adobe has said the scope of a cyber-security breach disclosed nearly a month ago was far bigger than initially reported.

The company has acknowledged that attackers obtained data on more than 38 million customer accounts.             

Adobe also said that hackers had stolen part of the source code to the Photoshop editing software that is widely used by professional photographers.          

The company disclosed the breach on 3 October, saying attackers took credit card information and other data from nearly three million customers' accounts.    

Adobe also said that the hackers accessed an undisclosed number of Adobe IDs and encrypted passwords that were stored in a separate database.

It has now revealed that about 38 million records from that database were stolen.            

The company reported that the attackers stole source code to three other products: Acrobat, ColdFusion and ColdFusion Builder.

Adobe spokeswoman Heather Edell said the software maker believes the attackers also obtained access to "many invalid Adobe IDs, inactive Adobe IDs, Adobe IDs with invalid encrypted passwords and test account data".

She said the company is still investigating to determine how much invalid account information was breached and is in the process of notifying affected users.

Even though the company believes the stolen passwords were encrypted, the attackers may have been able to access them in plain text by one of several methods, including breaking the algorithm that Adobe used to scramble them, said Marcus Carey, a security researcher and expert on cyber attacks.

They could likely use those passwords to break into other accounts because many people use the same passwords for multiple accounts, he said.             

"This is a treasure trove for future attacks," Mr Carey said.

Adobe spokeswoman Heather Edell said the company was not aware of any unauthorised activity on Adobe accounts as a result of the attack.             

However, she said she could not say whether stolen credit cards or passwords had been used to launch follow-on attacks against Adobe customers or conduct other types of cyber crimes.

"Our investigation is still ongoing," she said. "We anticipate the full investigation will take some time to complete."