Here at Lifehacker we're pretty keen on e-cards as a form of Christmas greeting, but it's worth reminding people that holiday cheer is also often utilised as a means of distributing spam and malware. AVG Technologies (whose free security software is amongst the top five anti-virus options favoured by Lifehacker readers) estimates that 500 million electronic cards will be sent this season, and its polling suggests that 74% of people will unthinkingly open e-cards. It's always tempting to open what looks like a message from family, but if your Brisbane-born mother has apparently described herself as "Mom", it's a safe bet you're dealing with an intruder. If you follow sensible security practices -- never opening attachments, deleting anything that looks even mildly unfamiliar, keeping your system patched, and running reputable security software -- you shouldn't run into trouble. It's also worth reminding friends and family of the same rules, lest you spend the holidays fixing everyone else's compromised PC.