San Francisco -- Cyber crooks are capitalizing on influenza fears with torrents of email promising "Swine flu" news but delivering malware or dubious offers for potency drugs or penis enlargement.

"Zombie" computers infected with a dreaded Conficker virus that became an online scourge this year are among machines being used to spew flu spam crafted to trick email recipients, according to computer security firm Trend Micro.

"The thing making it worse is the misinformation out there about swine flu," Trend Micro threats research manager Jamz Yaneza said Thursday.

"These guys have picked up on all the fears people have. With all the hysteria of swine flu, some people click on these emails."

Subject boxes of spam email feature lines such as "Swine Flu Outbreak!" and "Madonna Catches Swine Flu!" in order to grab people's interest in a tactic referred to by hackers as "social engineering."

The words "swine" and "flu" had essentially not been seen together in spam prior to the third week of April, David Marcus of McAfee said in a blog posting at the computer security firm's website.

The word combination surged in spam on April 27, with half the email apparently coming from sources in Germany, Brazil and the United States, according to Marcus.

McAfee said it has also seen keywords "swine" and "flu" used to direct Internet users to a Russia-based website booby trapped with a computer virus.

"Malware writers, spammers and scammers are low lives," Marcus wrote.

"They will use any high media event or high impact news story to push their wares including the sickness and misery of others. Stay vigilant and stay safe."

Crime groups involved with Conficker, Storm and other computer viruses that take control of people's machines and weave them into "botnet" armies are most likely behind the flu spam, said Trend Micro global director of education David Perry.