Cell phones can catch viruses when they download an infected file.

How They Spread

Phones that can only make and receive calls are not at risk. Only smartphones with a Bluetooth connection and data capabilities can receive a cell-phone virus. These viruses spread primarily in three ways:

  • Internet downloads - The virus spreads the same way a traditional computer virus does. The user downloads an infected file to the phone by way of a PC or the phone's own Internet connection. This may include file-sharing downloads, applications available from add-on sites (such as ringtones or games) and false security patches posted on the Symbian Web site.
  • Bluetooth wireless connection - The virus spreads between phones by way of their Bluetooth connection. The user receives a virus via Bluetooth when the phone is in discoverable mode, meaning it can be seen by other Bluetooth-enabled phones. In this case, the virus spreads like an airborne illness. According to TechnologyReview.com, cell-phone-virus researchers at F-Secure's U.S. lab now conduct their studies in a bomb shelter so their research topics don't end up spreading to every Bluetooth-enabled phone in the vicinity.
  • Multimedia Messaging Service - The virus is an attachment to an MMS text message. As with computer viruses that arrive as e-mail attachments, the user must choose to open the attachment and then install it in order for the virus to infect the phone. Typically, a virus that spreads via MMS gets into the phone's contact list and sends itself to every phone number stored there.

In all of these transfer methods, the user has to agree at least once (and usually twice) to run the infected file. But cell-phone-virus writers get you to open and install their product the same way computer-virus writers do: The virus is typically disguised as a game, security patch or other desirable application.

The Commwarrior virus arrived on the scene in January 2005 and is the first cell-phone virus to effectively spread through an entire company via Bluetooth (see ComputerWorld.com: Phone virus spreads through Scandinavian company). It replicates by way of both Bluetooth and MMS. Once you receive and install the virus, it immediately starts looking for other Bluetooth phones in the vicinity to infect. At the same time, the virus sends infected MMS messages to every phone number in your address list. Commwarrior is probably one of the more effective viruses to date because it uses two methods to replicate itself.

So what does a virus like this do once it infects your phone?