14 DAY TRIAL // It seems that spammers are dropping infected files like hot coals. People that are guilty for internet crime will always use tactics that are efficient, if one strategy is not effective, they will drop it. And here are two examples for you - the lottery spam-scam is as old as the web, yet they still use it. Why? Because it still works! And here's an opposite example - PDF spam was great to bypass spam filters, but it couldn't properly reach users, since people didn't bother too much with downloading the PDF file. Spammers noticed that it was inefficient, so PDF spam crashed and burned.
For a long time now, spammers have used infected file attachments to land viruses on people's machines to turn them into drones or for who knows what other purposes. Based on the fact that not all internet users have an anti-virus, they would send their messages in that way. However, now they're switching to infected sites. And here are two reasons why - if you infect a site, to land a virus on a PC, it will infect not only the unprotected machines of those clicking on links in spam e-mails, but also the computers of the ones that visit the site in any other way. Another reason would be the fact that virus protection is a lot better than it was some time ago. For example, Yahoo! uses Norton AntiVirus to scan file attachments. Before ANY Yahoo! user can download an attachment, the file is scanned, so, yes, that "blasted Norton AntiVirus" is keeping you safe without even having to install it on your machine. And Yahoo! isn't the only one providing this service. But that's not something new, they knew about that, it's just that they had nothing to replace the old tactic with.
In any case, upon realizing that infected files are not as efficient as the links to infected sites, they switched. This is just natural, whenever they find a better way of infecting computers, they dump the old strategies. Spam carrying links to malicious sites has reached 35% - this conclusion, like others in this article, is based on a MessageLabs study, that you may consult here.