Warning: Those "holiday e-greetings" you and your kids find in your email in-boxes may not all be from friends. "E-cards can spread cheer, cheesy humor, and, unfortunately, computer viruses," the Christian Science Monitor reports. "Spammers and hackers continually shift their strategies to match the calendar. And this time of year, they often hide behind season's greetings." The temptation to click on a friendly greeting is called social engineering. The Monitor quotes a Trend Micro expert as saying that the most successful email virus ever had the subject line "I LOVE YOU." One thing people should always do is check to see if the email has the name of the person sending you the greeting and that you know the person! Check out the article's sidebar for other tips for malicious e-card avoidance.