Ah, April 15. Is there a day on the calendar when reality comes home to roost? Not likely. That's why I find it fitting that in trolling for news this morning I learned that the thus-far ethereal reports of instant messaging attacks had finally hit a target. A big target.

Yesterday, news agency Reuters found a digital worm called Kelvir had penetrated its Reuters Messaging system, which is closely linked with AOL's Instant Messenger and Microsoft's (NASDAQ:MSFT) MSN Messenger, according to News.com. Fears of the worm spreading to other systems forced Reuters to temporarily shut its messaging system down. The company told News.com that there's no timetable for bringing the messaging client back online.

Kelvir is one of the three most widely detected IM viruses in corporate sites, according to IMLogic, which recently released a report stating IM attacks are up more than 250% over last year. Symantec (NASDAQ:SYMC) describes Kelvir as the latest in a series of IM virus variants that target MSN Messenger and Windows Messenger. It's a so-called "social engineering" attack that sends an instant message to the infected user's contact list that encourages the recipient to click on a URL, typically one labeled as "Picture of you." Clicking on the link downloads spyware and kicks off more messages to the newly infected user's contact list.

Akonix Software, a privately held provider of IM security software, has been tracking Kelvir and reports several corporate IM networks have already come under assault. Surely Reuters is the highest-profile victim thus far. And the success of this attack is likely to encourage similar threats.

That means it's probably time to check the locks on your digital doors, and only let in those you know. For example, clicking on unknown links, says Chad Wolfsheimer, network security chief for The Motley Fool, is like "opening the door to your home without first checking to see who's knocking." Similarly, anti-virus and other security software are also a must, Wolfsheimer counsels. But, in the end, he says, good, old fashioned Foolish sense is going to be the best defense. Well, at least until someone invents a hackproof Kelvir vest.

For related Foolishness:

  • Apparently you can't be too young to get involved in IM scams.
  • And you can make one heck of a living hawking spam. But doing so might land you nine years in the slammer.
  • There are big bucks in IM, too.

Fool contributor Tim Beyers is too scared to own a PC. That's why he writes all of his columns on his Apple PowerBook. How do you defend against digital miscreants? Share tips with other Fools at the Help with this STUPID computer! discussion board. Tim didn't own shares in any of the companies mentioned in this story at the time of publication. You can find out what's in his portfolio by checking Tim's Fool profile, which is here. The Motley Fool has a disclosure policy.