Companies are finding it tough to keep out new types of banking malware, which continue to get better following the bar-raising threat known as Zeus.
The malicious programs all aim to swiftly and secretly steal credentials for online bank accounts, with some specializing in making large, unauthorized wire transfers from businesses using the ACH (Automated Clearing House) system.
A study by the firm SecurityScorecard, which specializes in tracking a company's risk of intrusion, found more than 4,700 organizations that were infected by some type of advanced banking malware.
SecurityScorecard collected the data in part by using sinkholes, or computers that researchers control which are part of a network of infected machines, known as a botnet. An analysis of those sinkholes can lend insight into how many machines may be infected with a particular type of malware.
The company also looks at spam campaigns, vulnerabilities in web applications, malware campaigns conducted using social media and monitors underground hacking forums, said Alex Heid, chief research officer.
"For hackers, you always want to look for the weakest link and pivot in," he said.
The study, conducted over the first five months of this year, found 11,952 infections affecting 4,703 organizations. Some of those organizations are customers of SecurityScorecard, while others are partners of those customers.
When SecurityScorecard evaluates a customer's network, the customer also shares information about their partners, who may also have access to their systems.
It's those relationships that are increasingly being targeted by hackers. Target and Home Depot both attributed large payment card breaches to the infiltration of third-party contractors whose credentials gave access to their systems.
The top banking malware families that have been circulating are Dridex, Bebloh and TinyBanker, Heid said.
Dridex spreads through spam that contains attachments to malicious XML files or Microsoft Office documents with macros, he said. Bebloh is hard to detect since it makes few changes to the computers it infects. TinyBanker -- named for its small 20K size -- is hard to find as well since its creators often change its digital footprint, which allows it to evade security products, he said.
Those distributing malware try to make sure their programs are FUD, or fully undetectable. They do that by using tools to encrypt the software called crypters or packers, which compress the file in a way that makes it hard to detect, Heid said.
SecurityScorecard also found instances of Dyre, another banking malware program that descended from the infamous Zeus software.
The U.S. Department of Justice, working with security researchers, managed to shut down the Gameover Zeus botnet in mid-2014. The botnet and associated malware stole as much as US$100 million.
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