Targeted attacks that utilize vulnerabilities in popular document file formats and execute via hard-to-find shell code are becoming an increasingly popular menace, according to researchers at IBM's Internet Security Systems division.

Experts working with the ISS X-Force group said that they've seen a rapid increase in the volume and variety of shell-code execution attacks leveled at their customers over the last 12 months.

Among the types of files most frequently assailed in the attacks are the most common types of documents passed around many organizations today, including Microsoft Word, Excel and PowerPoint formats, as well as Adobe PDF files.

Many times, the infected documents are being distributed inside specific organizations by hackers who disguise the threats as legitimate files being disseminated within a business via e-mail. Unlike many Web-based threats, the seemingly-innocuous documents typically give no warning that they actually carry malware code.

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