Tech crime has a new victim – the tech criminal. It appears that one form of attack that struck fear into the hearts of security experts the world over is actually a dud.

Symantec has noted a sharp decline in distributed denial of service (DDoS) attacks, where a network of remote-controlled bots - usually end-user machines infected with malicious software - overloads a target's system and takes it offline.

Tech criminals have instead turned back to old-fashioned spam to make everyone's lives a misery.

The decline in DDoS attacks is due to the fact that such attacks simply aren't paying off for the attackers, Symantec security engineer Yazan Gable said in a note on the company's website.

"Although there are likely a number of factors at play here, I think there is one primary factor: denial of service extortion attacks are no longer profitable," Gable wrote.

DDoS attacks first started to skyrocket in the second half of 2005, according to Symantec's twice-yearly Threat Report, rising 51 percent to an average of 1,402 attacks per day.

In the first half of 2006 the upward trend continued, reaching an average of 6,110 attacks per day.

But by the second half of 2006 DDoS attacks appeared to have reached a peak, declining to an average of 5,213 per day.