Corporate blogs are increasingly becoming an important part of the digital marketing mix, but at Cisco that mix just turned toxic with revelations that one of its in-house lawyers now stands accused of libel because of comments he made about so-called "patent trolls" on his blog.

According to an article in Business Week, the trouble began last May when a blog called Patent Troll Tracker came on the scene. True to its name, the anonymous blog focused on identifying so-called patent trolls -- those who buy patents with the intention of profiting solely from litigating patent disputes with major corporations.

By all accounts, the blog was a success. In fact, the blog was so widely read that attorney Raymond Niro Sr., the subject of a death threat posted in the blog's comments section, offered a $15,000 reward to anyone who could unmask the blogger. Later, Rick Frenkel, in-house patent counsel at Cisco, identified himself as the blog's author.

Though Cisco didn't sanction the blog, T. John Ward Jr. and Eric M. Albritton, two patent lawyers who were the frequent subjects of posts on the blog, filed suit against both Cisco and Frenkel alleging libel.

While the particulars of the case may matter only to the patent community, the ripple effects could be far reaching. Cisco sanctions 12 in-house blogs, which are written by about 75 workers. By comparison, Sun Microsystems has about 4,000 employees blogging, and Microsoft has tolerated an insider blog, dubbed "Mini-Microsoft" for years.

For its part, Cisco says it's working on new guidelines for employees who blog.