Criminals are counting on the circles of friends nurtured by social networking sites to make a killing -- ugly MySpace pages notwithstanding

Social Networking Accounts Prized By Cybercrooks - washingtonpost.com Security Fix

In an analysis of cyber crime activity in the 2nd half of 2007, security vendor Symantec Corp. found that two social networking sites together were the target of 91 percent of U.S.-based phishing Web sites. Social networking sites also were the leading targets of phishing sites located in four other countries listed by Symantec in its phishing Top 10.

Hijacked social networking pages often are used to host malicious software or "malware" directly or to host links phishing or malware sites that are then advertised in messages sent to all of the contacts in the victim's social network.
Keep those Facebook credentials close to your chest!