With more valuable data than consumers and far fewer security defenses than their large enterprise counterparts, small and midsize businesses have become a favorite target of malware authors around the world.

"SMBs have a hard challenge," says Neil Daswani, CTO of Dasient, an anti-malware services vendor. "Their customers often expect the security guarantees that a large company would give them, but SMBs typically don't have the infrastructure of their own to provide that level of security."

Whether their computers are being controlled by botnets, their information is being stolen through a Trojan kit, their websites are infecting customers with malware, or their Web application flaws are being exploited to steal products, SMBs face malware-related attacks from all corners. Let's look at three of the biggest threats coming from malicious code and how SMBs are dealing with them.

1. Zeus Attack Tool Kit
Preconstructed attack software, such as the dreaded Zeus toolkit, has revolutionized the cybercrime "industry," experts say.

"Attack toolkits have lowered the bar so that anybody with even a limited amount of technical skills can get in the game -- and [these toolkits are] certainly driving the vast amount of malware that we're seeing today," says Kevin Haley, director of Symantec Security Technology and Response.

No kit has caused as much damage as the Zeus toolkit, says Chet Wisiniewski, senior security adviser at Sophos, who says Zeus-based attacks have been one of the biggest threats to small businesses during the past two years. That threat is only going to get larger now that the source code to this kit was leaked, effectively turning it from a crimeware package costing $400 to $5000 into a freeware offering.

"In particular, small businesses are targeted specifically by this because Zeus was built to harvest banking credentials -- and what the bad guys have figured out is that small businesses are the perfect victims," Wisniewski says. "If they go after you or me, one, we have less money, and, two, we have 30 days with our bank to reverse the fraudulent activity."

That's not so with SMBs, which usually have only 48 hours. "That's a problem for small businesses because most people aren't watching every transaction like a hawk like that," Wisiniewski says.

Installing antivirus software is the first step to protecting an SMB from Zeus attacks, but that's only a start, experts warn.

"Having good spam filtering not only reduces the annoyance of your mailbox filling up, but can also shrink your attack surface because if the email doesn't show up in your mailbox, it doesn't matter if you have a tendency to click on things you shouldn't or not," Haley says. Organizations should start limiting employees' access to corporate banking account information, reducing the chance that they'll give it away to social engineers, he advises.

Additionally, SMBs should be practicing good patching hygiene and doing a better job of inspecting the content that crosses their endpoints, experts say.

"And don't focus only on patching the operating system and the Web browser -- look at browser plug-ins such as Java and Adobe Reader. These are the top two outdated components that are targeted by attackers," says Michael Sutton, vice president of security research for Zscaler.

"Leverage inline solutions that can inspect content," Sutton advises. "These solutions do not have to be expensive. Thanks to SaaS-based solutions, there are offerings available that are paid on a per-user basis and are available to all companies at an affordable price, regardless of size."

Next: Unwitting malware distributors.

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