Computer users are becoming wiser about opening attachments from unknown email sources and so they are beginning to slow down.
BitDefender's researchers have determined that the number of spam messages sent to recipients with PDF attachments has recently decreased, and they believe this can be attributed to the relative ineffectiveness of this spamming method, as it requires more user interaction than usual e-mail spam.

BitDefender's researchers regularly monitor spamming activities using BitDefender's proprietary outbreak detection technology, which can automatically detect new types of spam e-mails and create "signatures" later used by BitDefender security software to block them.
"We detected a peak in this type of spam about two weeks ago, but the whole wave was relatively short-lived," says Vlad Valceanu, head of BitDefender's antispam lab. "End users are finally becoming skeptical to opening email attachments from sources not familiar to them. As a result, it appears spammers are giving up on this tactic."
The PDF spam wave noticed by BitDefender Labs several weeks ago was mainly comprised of fake stock tips, supporting penny stock "pump-and-dump" schemes. It raised concerns in the corporate world because text-based antispam solutions could not accurately filter such content, while blocking PDF attachments at the corporate gateway was definitely not an option.
"While spammers are sending out fewer attachments with their emails, we don't expect to see a dramatic decrease in the overall amount of spam distributed," adds Valceanu. "Our research has simply found that spammers are finding newer, more productive methods in their delivery of spam messages. PDF spamming will likely cease to represent a significant percentage of the spam flow in the weeks and months to come."