To give you an idea of where malware originated and how it evolved into the advanced and persistent threats piggybacking off today's most popular social networks, Trend Micro researchers have developed a timeline of history's most infamous malware.
Social Attacks Era
There are 3.5 new threats per second (almost 12,600 per hour), 1/3 of web users are attacked by cybercriminals using social networking sites to target victims. (Source: nsslabs.com)
Web Threat Era
In the underground economy, a person's credit card number is worth between $7 and $25 US. Trend Micro saw a 2,135% Increase in web threats from 2005-2008. Ninety-two percent of Digital Threats arrived via the Internet in 2008.
Worm Outbreak Era
An outbreak is the propagation of the same security threat into different computers within a relatively short period of time. There were 30 major outbreaks with 16,880 Malware detections and more than 37,000,000 infected files in 2004.
Virus Era
Computer Viruses are created for personal gain (notoriety) research projects, fun, pranks, vandalism etc. Others are made for Program improvements.
Scammers and cybercriminals take advantage of the element of trust on social networking sites and target the most popular features and sites. Trend Micro researchers created an overview of the locations with the lowest risk to the ones with the highest.
Cross-Posts: Shortened links from other social networking sites like Twitter may lead somewhere else.
Events: Spammers "invite" targets to events. Regardless of their response, users unwillingly spam the same event to their contacts.
Chat: Bad Contacts can automate replying to users, apart from sending bad links.
Bad Friends: Malware like KOOBFACE variants create bogus accounts and automatically add people to the list of users' friends.
Apps: Some apps request for access to more personal information than is necessary.
Wall Posts: Users are asked to visit pages to see any of the following: