Security analyst Brian Krebs this week posted a list of 760 companies that may have attacked by malware, CNN Money reported Thursday.
In his blog, Krebs said the information came from a server that had been breached and used to control compromised personal computers.
CNN Money said the list of hacked companies included 20 percent of Fortune 100 firms as well as the European Space Agency, the Internal Revenue Service and the federal government's General Services Administration.
Krebs said Internet service providers like Comcast, Verizon, AT&T, Sprint and Windstream, which appeared on the list, may not have been attacked but subscribers on their networks were.
The list of organizations affected was recently presented to Congress, CNN Money said.
"There has been lots of handwaving," Krebs told CNN Money, "but people just aren't sure of what to make of these advanced persistent threats of this scale. If my blog post does anything, it's to get people to pay attention to it."