A growing number of PlayStation gamers have complained of being locked out of their online accounts.
In the past 48 hours, more than 100 PSN members have contacted Sony via one of its UK Twitter accounts - just one of several ways to reach the firm.
Many suspected their logins had been hijacked. Some of those who regained access said funds were now missing.
Sony told the BBC that the PlayStation Network had not been hacked and pointed to other potential causes.
"We routinely monitor for irregular activity, and if such activity is detected, we may sometimes reset passwords of affected accounts to protect users and their account information," Sony said.
"We strongly advise users to keep a close eye on their accounts for unusual activity and avoid entering your username/password into unofficial sites looking to phish credentials based on fake promotions."
On Twitter, the firm has apologised for the delay in reinstating accounts and says that the company helpline is "particularly busy at the moment".
Cybersecurity expert Prof Alan Woodward said if there had been a breach, the leaked data would probably have appeared elsewhere.
"There are two ways this could happen: either someone has got into Sony's central systems, which have been compromised before, or people's individual systems have been compromised," he told the BBC.
"If there had been some kind of central breach, the dark web would have been alight with it and we in the industry would be aware of it by now, I have not seen anything.
He added that if individual accounts had been breached and Sony had reset their passwords then users would expect to be notified by email.
"The fact they haven't suggests that usernames and passwords have been given away unintentionally," he said.
"Clearly if someone is spending money it is criminal activity."
Sony was unable to clarify how many users were affected and the issue only appears to be affecting PlayStation users in the UK.