Social networking sites let us contact old friends, make new online buddies, or journal about our latest personal news. But reaching a common ground between openness and privacy is a constant battle. The bottom line: you cannot be sure who is reading your posts, or accessing the personal information that you put on the web.

Last week, a Californian teenager found this out the hard way when her MySpace post depicting her displeasure of the war in Iraq, with a picture of the U.S. president and the title "Kill Bush," brought the Secret Service to her high school molecular-biology class. The ironic twist: the Internet never forgets. The young woman had removed the post last spring, after learning in her 8th grade history class that such threats are a federal offense, but U.S. federal authorities saw the page, and placed her on their checklist.

The popularity of online social networks is bringing up more and more privacy and security issues, as everyone uses these sites to their advantage, from bloggers to advertisers to vendors of spyware and malware.

Even if you are careful not to put personal details in online profiles, you may be allowing malware and spyware, which is prevalent on social networking sites, into your system unintentionally. According to an August report from the web security company ScanSafe, up to one out of every 600 profile pages on social networking sites host malware.

If you need to use online networking sites to stay connected, our advice is to use common sense and caution every time you post a message or create a profile; never post information that you would not feel comfortable with others seeing. Also, make sure your computer is secure with anti-virus software, anti-spyware software, and a firewall.