Malware writers are ramping up their use of commercial file hosting sites and cloud services to distribute malware programs, security researchers said at this week's Black Hat conference here.
Traditionally, malware writers had distributed their malicious code from their own sites.
But as security vendors get better at detecting and blacklisting those sites, hackers are increasingly distributing their malware products from legitimate host sites. The technique has been used a bit for more than two years, but now appears be gaining steam, researchers said.
Often, the owners of legitimate sites fail to properly scan the content they are hosting, which allows attackers to furtively post malicious code with relative ease, said Michael Sutton, vice president of research at ZScaler, a provider of cloud-based security services for enterprises.
Malicious content distributed from a legitimate site is more likely to make it past corporate defenses. Vendors are also unlikely to blacklist a legitimate hosted service, allowing malicious content hosted on one to stay up longer, he said.
Zscaler said he's heard reports of malicious files hosted on Dropbox, but the they appear to have been removed, the blog noted.
Sutton pointed to recent incidents were attackers posted and distributed malicious code on Google Code and Dropbox as an example of the trend. A blog on Zscaler's website lists nearly three-dozen malicious files hosted on the Google Code site, which contains tools for software developers.
The message for IT managers: Don't blindly trust domains that seem to be secure, Sutton said.
"Attackers are starting to leverage hosting services" to stage malicious code, he said. "It used to be that [attackers] would set up their own servers," to host malware. "Then we saw them infecting legitimate third-parties. Now they are using hosting services. They are no longer paying for hosting [malware] and are less likely to get blacklisted."
Meanwhile, Firehost, a provider of cloud-hosting services for enterprises, has seen an increase in Web application attacks originating from the networks of legitimate Web hosting services, said CEO Chris Drake.
In its latest quarterly security review, Firehost observed a noticeable increase in the number of SQL injection attacks, directory traversal attacks and other Web application attacks launched from within cloud service provider networks, Drake said.
Cloud providers often have weak validation procedures when signing up new customers, allowing attackers to create accounts with fake information. The accounts are then used to deploy and administer powerful botnets that run in the cloud infrastructure, he said.
In the second quarter of 2013, the IP filtering system that Firehost uses to protect its customers against malicious attacks blocked about 1.3 million unique attacks. Of the total, a noticeable number of attacks originated from IP addresses belonging cloud services companies, Drake said.
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