85 more stores are being added each day to the total; The US National Republican Senatorial Committee is the largest target.
Hackers have installed skimming scripts on more than 6000 online stores and are adding 85 each day in a wide-scale active operation that may have compromised hundreds of thousands of credit cards.
Dutch developer Willem de Groot found the malware infecting stores running vulnerable versions of the Magento ecommerce platform.
Attackers uploaded scripts which would capture and ship credit cards from online shops to Russia-based command and control servers.
The US National Republican Senatorial Committee is the most high profile scalp the campaign after an unknown number of credit cards were stolen from supporters buying merchandise and offering donations through its online store.
The Committee did not answer questions by The Register on remedial actions it had taken nor whether it could guarantee customer credit cards were safe.