"The sniffer malware that surreptitiously siphoned tons of payment card data from card processor Heartland Payment Systems hid in an unallocated portion of a server’s disk. The malware, which was ultimately detected courtesy of a trail of temp files, was hidden so well that it eluded two different teams of forensic investigators brought in to find it after fraud alerts went off at both Visa and MasterCard, according to Heartland CFO Robert Baldwin.
“A significant portion of the sophistication of the attack was in the cloaking,” Baldwin said.
Payment security experts pretty much agreed that hiding files in unallocated disk space is a fairly well-known tactic. But it requires such a high level of access—as well as the skill to manipulate the operating system—that is also indicates a very sophisticated attack. One of those security experts—who works for a very large U.S. retail chain and asked to have her name withheld—speculated that the complex nature of the hiding place, coupled with the relatively careless leaving of temp files, could suggest a less-skilled cyberthief who simply obtained some very powerful tools."