The number of households in the United States that rely solely on mobile phones continues to increase. As of July 2011, 31% of households had mobile phones and no landlines. Additionally, almost one in six households used mobile phones exclusively or almost exclusively, despite still having a landline.

This is the first time that adults (of any age range) have been more likely to go without landlines. Most likely, in one to two decades, the landline will be as obsolete as the rotary phone is today.

With almost half a billion smartphones shipped, sales of smartphones in 2011 outnumbered sales of all PCs. Tablets are counted as PCs, but they run Google Android and Apple iOS software just like smartphones do. If you add together smartphone and tablet sales, it’s clear the mobile device market is much larger than the traditional PC market.

The growth in sales volume of both smartphones and tablets creates a huge audience for mobile device software developers, both commercial and criminal. And since cybercriminals go where the numbers are, they are moving their attacks to mobile devices.

Whenever there’s a major transition in technology, the uncertainty and newness create a perfect opportunity for scammers to launch attacks. Hackers and other criminals are seizing the opportunity, creating swindles, malicious apps and viruses that suit their criminal purposes. And there’s no reason to expect them to stop before some other technology nudges aside mobile in popularity.

There are approximately 40,000 viruses targeting the Android operating system today. In Android’s young life, that’s astounding compared to a similar lifespan dating back to when Microsoft Windows was first launched.

So you need to make sure you protect yourself, because for most of us, our mobile devices are our most personal computers. Here are some things you should do to protect yourself:

Use a PIN to lock your device and set it to auto-lock after a certain period of time

Only download apps from reputable app stores, and review the app permissions to make sure you’re comfortable with what information on your device the app can access

Don’t store sensitive information on your phone like user names and passwords

If you use online banking and shopping sites, always log out and don’t select the “remember me” function and don’t access these site when using free Wi-Fi connections

Regularly review your mobile statements to check for any suspicious charges. If you do see charges you have not made, contact your service provider immediately.

Never respond to text or voicemail with personal information like credit card numbers or passwords

Never click on a link in an email, social networking site or message from someone you do not know

Use mobile devices security like McAfee Mobile Security, or McAfee All Access which protects all your devices

Robert Siciliano is an Online Security Expert to McAfee. He is the author of 99 Things You Wish You Knew Before Your Mobile was Hacked! (Disclosures)