Two recent events, one local and one national, underscore "private" digital communication's vulnerability to wider audiences than is expected or wanted.

A pre-dawn, head-on collision involving an allegedly drunken driver that killed a Bakersfield teen and injured her three passengers took on an unfortunate taint when Twitter posts revealed the victims may have been involved in drinking games that night. And the re-election of Barack Obama inspired a deluge of racist and potentially felonious social-media postings across the U.S. Many went viral, embarrassing the posters -- in at least one case costing someone a job.

But those missteps were, for the most part, made by young, naive people. We can't say the same for the current scandal involving two of the highest-ranking military men in America, as well as two intelligent, savvy-seeming adult women.

Retired Gen. David Petraeus, the former CIA director, and Gen. John Allen, the top NATO commander in Afghanistan, are being investigated for unseemly conduct, if not potential breaches of national security, after their private email exchanges with two women suggested behavior that was questionable at best. The scandal goes well beyond embarrassment for the parties and families involved; it threatens to drag down Obama's second-term transition plans.

There are two lessons here. One, even astute men and women can misjudge the security of their private communications. Sophisticated hackers have proved that many times. And, two, civil libertarians are right. Law enforcement's power to police the Web for crime, espionage and sabotage means the professional and private lives of Americans are unavoidably subject to exposure.

That Petraeus, the nation's top spy, could fall victim to this consequence of modern investigation underscores its pervasive truth. Any illusions that online communications exchanged in the privacy of one's home are secure are just that -- illusions.