KnowEm.com (http://knowem.com) launched a new web service today which monitors hundreds of popular websites for social media identity theft. By entering a username, which can be a brand name, internet identity, or vanity URL, KnowEm.com allows you to instantly monitor the availability of that username on over 120 popular social media websites such as Twitter, MySpace and Digg.

“Social Media identity theft is the modern form of domain name squatting,” says KnowEm co-founder, Barry Wise. “10 years ago it was a race to get CompanyName.com. Today it’s a race to secure a brand name on sites such as Twitter, which is quickly becoming an amazing tool for both brand transparency and customer service.”

A quick check today revealed that some of the biggest brands in the world have still not secured their account name to protect their brand from identity theft. For example, Google (NASDAQ:GOOG), Pepsi (NYSE:PEP), Microsoft (NASDAQ:MSFT), Exxon (NYSE:XOM) and Citigroup (NYSE:C) still show that dozens, and in some cases over 80%, of popular social media websites still list their brand names as available account names.

It’s not just major media brand names that have dropped the ball — many celebrities have not secured their online identity either. Ashton Kutcher and Oprah Winfrey’s recent exposure on the popular new microblogging service Twitter.com has shown that celebrities are taking interest in using social media as a vehicle for PR and communication. But as of today their Twitter screen names, @aplusk and @oprah, are still both available on almost 90% of other websites on KnowEm.com’s list.

“The time is coming when online reputation management is critical even for normal citizens. You would be surprised how many companies are now using Google to see what a prospective hire has about them on the internet,” says Knowem co-founder, Michael Streko. “It is just too risky to let your name fall into the hands of someone else.”

KnowEm not only monitors to see if your username is available on 120 sites, it also offers a commercial service which will register your brand or username for you. For $64.95 you can secure your identity on over 120 different social media websites. For an additional $9.95 per month, they will also continue to monitor new websites and register your username on them as soon as they launch.