Many employers use search engines and social media to discover information about prospective and current employees. In some cases, that information, especially social media information from sites like Facebook and Twitter, has been used to not hire candidates for a job or to fire employees.
However, there are potentially discrimination issues involved. It's also time consuming for hiring managers to research employees themselves. Social Intelligence Corporation (SIC) addresses both issues by providing in-depth background checks for employers that includes online research from social media and other internet sites and complies with the Fair Credit Reporting Act (FCRA) and anti-discrimination laws.
It's important to note that this service makes it even easier (and quicker) for employers to find out information that can be held against you when you're job searching or on the job. It's really important to be careful what you post on social media, blogs, and other internet sites.
The chances of someone finding information that could be damaging to your career are high. Your best bet is to be careful about what you post and to presume that what you post is public, despite any privacy settings you may have.
Here's more on social media background checks and how they work.
Related: Social Media