Covert agencies--as well as corporations--are searching email files for words and phrases that may reveal incipient (or ongoing) criminal activity. The 911 terrorists knew this, which is why they emailed one another in code.
Aside from the words one might expect them to look for, such as "bomb" or "attack," corporate CEOs searching their employees' files for fraud look for words and phrases like "nobody will find out," "cover up" and "off the books." With the type of linguistic software out there, it's hard to keep secrets anymore (NOTE: Subscribers can still listen to this audio).
Linguistic analysis software can flag uncharacteristic changes in tone and language in electronic conversations and can also be tailored for particular types of employees, especially stock traders.
In the January 7th edition of the Financial Times, Jennifer Thompson writes that "more than 3,000 such words and phrases used in email conversations among employees engaged in corporate wrongdoing have been identified through specialist anti-fraud technology." Thompson quotes corporate fraud investigator Rashmi Joshi as saying, "The language, which is a mix of accounting phrases, personal motivations and attempts to conceal (NOTE: Subscribers can still listen to this show) are very revealing."
The lesson from all this? If you want to do something nefarious that you don't want your boss to know about (or even give him or her a surprise birthday party), you need to do it the old-fashioned way: Put on your fedora and trench coat and meet your accomplice in a dark, out-of-the-way bar to discuss it over a couple of shots of rye.