The exploit enables malicious programmers to specially format an e-mail to be sent as a text message by setting the message's Protocol Identifier to "Internet Electronic Mail." If the message contains more than 32 characters, certain S60 devices would not be able to receive other SMS or multimedia messages. Depending on the handset, the vulnerability could damage the targeted phone with a single message.
Millions of handsets were potentially vulnerable to this exploit, including UIQ devices and handsets running S60 2nd Edition Feature Packs 2 and 3, S60 3rd Edition, and 3rd Edition Feature Pack 1. Nearly any device capable of sending SMS as "Internet Electronic Mail" can send a malicious message.
Users who are vulnerable to this exploit can download an SMS Cleaner from Nokia. Once installed, the application will cleanse the device of malformed messages and restore the functionality of the messaging system. Once the application has completed the process, it will restart the phone and uninstall itself.
The exploit was discovered by researcher Tobias Engel an independent researcher who made his findings known to F-Secure, and later made public at the Chaos Communication Congress event last year. The security firm said it made Nokia aware of the exploit months before it was exposed, and it sold software that protected users from the vulnerability.
While there hasn't been a widespread attack on smartphones, most security experts believe it's a matter of time with vulnerabilities showing up for high-profile devices like the iPhone 3G and the T-Mobile G1. InformationWeek recently took a look at how enterprises can incorporate smartphones to boost productivity while making sure the data is secured, and the report can be downloaded here (registration required).
The article was edited on 1/30 to clarify Mr. Englel's relationship to F-Secure.