Spam and virus threats to enterprise messaging security and compliance may level off this year compared to 2007, but social engineering techniques are evolving to challenge businesses and security software providers, according to a new report released by Google's Postini team.

The report, released March 6 after Google's Postini team commissioned the study to survey 575 IT professionals, found that Postini data centers recorded 57 percent more spam and virus attacks in 2007 compared to 2006.

The size of spam e-mails also increased considerably as spammers included images, .pdf files, documents, spreadsheets and even multimedia files to spoof spam filters, according to report author Adam Swidler, senior solutions marketing manager for Postini.