Trend Micro said it identified around 1,050 new computer worms, viruses, Trojans and other examples of malware in May, compared to 1,700 the month before. However, the company said despite the decrease, "actual virus activity remained high".
IDC analyst Megan Dahlgren says the results show that hackers are recycling the old codes.
"They are exploiting already existing malicious code and reintroducing it into a new environment," she said.
According to Trend Micro, all of the top ten virus threats of May were worm-related, confirming, they say, that this type of malware is still the biggest threat to corporate networks and home users.
Dahlgren says the reason behind the worm's popularity is that viruses and Trojans are more visible in their infection.
"It's harder to get viruses and Trojans out there; that's why worms are more popular, they are much more undercover and they're global," said Dahlgren. "Also if a worm gets in it can do a lot of damage very quickly."
Trend Micro issued three outbreak warnings in May, with its first red-alert warning over the Sasser worm attack, followed by two yellow alerts raising caution to the Sasser A variant and Wallon A worms.
The company says the surge of worm outbreaks illustrates the need to have updated operating systems and applications, and also to have the appropriate Microsoft security patches installed.
Trend Micro also reiterated the warning that "traditional antivirus solutions alone can no longer deal with these threats," saying companies need to implement "holistic" solutions to combat the evolving threats online.
Dahlgren says the focus for corporations now is to identify their vulnerabilities and keep ahead of the hackers.
"It's a matter of addressing the old vulnerabilities and identifying the new," she said, adding "it's a more complex issue than just employing an antivirus software solution; it's about asset management more than anything else."