Digital desperadoes have begun hiding their larcenous activities behind blizzards of spam aimed at their victims' inboxes, a report released Tuesday by a cloud security provider notes.The technique, called Distributed Spam Distraction (DSD), began appearing early this year, AppRiver revealed in its Global Threat & Spamscape Report for the first half of 2013."This technique is highly targeted towards a specific individual, and is difficult to block in its entirety," the report said. "It's also difficult to understand if you have no idea what is happening."Spam attacks may last from 12 to 24 hours, it continued, and inundate an inbox with as many as 60,000 messages. The purpose of the assault is to prevent a target from reading their legitimate email."The people behind this spam blast have somehow obtained personal account information for their target as well as their proper email address," the report explained."In order to hide account transaction information confirmation emails, such as purchase receipts or balance transfers which now arrive instantly via email, the attackers, just before they make the illegal transactions, turn on this deluge of spam email in order for these very important emails to get lost in the flood," the report said.Unlike much of the malicious spam circulating on the Internet, messages in a DSD attack don't contain any malicious links or attachments. "They keep them as simple as possible to help evade certain types of detection," Fred Touchette, a security analyst with AppRiver, told CSOonline.To stop these, he continued, you have to block them based on content. That can be hard to do when the text in the messages is randomly chosen from books.At this point, the tactic isn't widely used. "It's not a widespread technique, but I have seen it many times throughout the last few years," Touchette said. "It requires more work than many criminals are doing in this age of specialization."[Also see: Fruity Instagram spam dies quickly on the vine]The AppRiver report also noted that smartphones running Google's Android operating system account for more than 90 percent of all mobile-device malware.Trend Micro is predicting there'll be more than a million samples of mobile malware in the Android market by the end of the year -- four times last year's number."While some threats still exist for the Symbian OS, those threats are on the wane," the report said. "Malware writers appear to be now focusing their efforts almost exclusively on Android devices with the total number of malware variants more than doubling over the past year."While the security industry has been issuing dire predictions for months about mobile malware, those warnings don't appear to have raised too much concern among users. "I don't think it's affected enough people for its concern to be widespread," Touchette said.That's likely to change, however, especially as online banking functions move to mobile devices. "A lot of consumers are using mobile banking now, but the banking industry has stopped short of allowing robust payments," George Tubin, a senior security strategist with Trusteer, said in an interview."But the marketing folks in banks are pushing for more payment capabilities," he continued. "The fraudsters will jump in once these companies get more payment capabilities out there."In addition, a lucrative line of income for web predators on the PC -- ransomware -- has been moving to the mobile sphere. "Ransomware has shifted significantly from PC focus to unprotected mobile devices," JD Sherry, vice president of Technology and Solutions for Trend Micro, said in an interview.In its mobile form, a splash screen will appear on the display of an infected phone declaring cell service will be cut if a ransom isn't paid. "That's a huge trend that I see spiking in the next six months," Sherry said.Although there haven't been any radical changes in the last six months, network marauders appear to have modified their tactics. "There's a lot more focus on compromising the user than compromising the user's machine," said Nick Levay, CSO of Bit9."If you can get a user's legitimate login credentials, you don't need to put malware on their machine, so social engineering attacks is something we continue to see growth in," he said.