Until recently, the damage caused by spam was restricted to wasting users' time, companies' productivity losses due to employees having to check and delete messages and problems with network performance due to excessive junk mail, Panda said.
But spam has evolved and is now becoming a serious threat with potentially disastrous consequences because cyber-crooks are using the medium to propagate phishing attacks, Panda warns.
Luis Corrons, director of Panda Software's labs said: "It would seem that phishers are now using the know-how accumulated by spammers over the years to hit as many potential victims as possible with their fraudulent emails."
According to Corrons, zombies – malware infected PC's that are controlled remotely - are now the most widely used method for sending spam.
It is important to periodically check computers to ensure that they have not become zombies at the command of criminals, said Corrons. Bots are usually installed on systems in such a way that users are unaware of their presence. Bots not only cause problems for those receiving spam, but also for the owner of the infected computer - any investigation will lead directly to the zombie computer, while the real attacker's identity will remain unknown.