According to PCPro, there are now 24 pages of angry user postings on Apple's own forums, all from iTunes users whose accounts have been compromised.
The problem, says Stewart Mitchell, has seen iTunes users' gift certificates on the service drained away.
"It's unclear at this stage whether the action is the result of a widespread hack on iTunes or whether individual accounts have been hacked, but more consumers appear to be falling victim to the attack", says PCPro.
"From the number of postings here, obviously, Apple has a big problem with either account security, in-app purchase fraud, or both", adds the tech newswire.
Dr. Mitchell goes on to say that hackers are changing iTunes' billing addresses, and then use games and in-app purchases to route money out of the iTunes account.
"The problem appears to have been active since late last year, but the number of complaints has swelled dramatically since May, and some victims claim to have been attacked more than once", the newswire notes.
PCPro quotes a posting from a Colorado iTunes user and his wife who had their gift card credits stolen by in-app purchases, wiping out the $22.98 remaining credit on their account.
The in-app purchasing system on the iOS platform was only introduced on a wide scale by Apple this spring, but it seems that hackers have wasted no time in attacking iTunes users, Infosecurity notes.
PCPro, meanwhile, reports that Apple has yet to respond to requests for information on the case, "leaving users to speculate on the scale and severity of the issue, but Sega has confirmed it is investigating the reports."
"It is very likely that your iTunes account has been stolen and is being used by someone else to purchase items in this game," Sega is reported to have said in its forum.
"We are currently investigating this claim as well as some others, but since we have no access to any customer's iTunes account information or transaction histories we highly recommend contacting Apple directly", the company added.