Carlos Enrique Perez-Melara, who allegedly created malware purporting to catch out cheating lovers, has made it on to the FBI’s “most wanted” list of cybercriminals.

The FBI says Carlos Enrique Perez-Melara ran a website offering customers a way to “catch a cheating lover” by sending spyware masquerading as a greeting card.

Opening the card downloaded the malware on to the recipient’s computer and recorded keystrokes and messages.

The “Lover Spy” program cost $89.

Carlos Enrique Perez-Melara was indicted in July 2005 but has avoided capture ever since, only now making it on to the FBI’s most wanted list.

He ran the operation from his San Diego home in 2003, the FBI says, while he was in the US on a student travel visa.

Carlos Enrique Perez-Melara allegedly created malware purporting to catch out cheating lovers

The charges against Carlos Enrique Perez-Melara, 33, included making, sending and advertising an interception device, and unlawfully intercepting electronic communications.

The indictment said Lover Spy was designed “with stealth in mind, claiming that it would be impossible to detect by 99.9% of users”.

But Carlos Enrique Perez-Melara has avoided the authorities ever since and his last known location was San Salvador, the FBI said.

The agency appears to have added the hacker to its list partly out of frustration at his elusiveness.

“These are sophisticated folks who know how to hide themselves on the internet,” said John Brown, who oversees the FBI’s cyber-division.

The agency has offered a $50,000 reward for information leading to his arrest.

According to the 2005 indictment, Carlos Enrique Perez-Melara sold the malware to 1,000 customers, who then used it to infect the computers of about 2,000 victims.

Victims took the bait about half the time, the government said.

People who bought the spyware were charged with illegally intercepting electronic communications.