Criminal hackers are increasingly deploying hybrid worms engineered to steal confidential information from unwitting internet users, security experts warned today.

Panda Security said that worms comprised 17.6 per cent of all malware infections in February, up from 15 per cent in January.

Trojans accounted for 23.7 per cent of infections and have remained steady for the past several months, but worms have increased for the second month in a row.

The new generation of worms are increasingly sophisticated, and are capable of acting in Trojan-like ways.

"The worm boom is caused by an increase in their capabilities. Until recently, most worms were solely designed to spread from one computer to another," said Luis Carrons, technical director of PandaLabs.

"Over the past few months, however, there has been an increase in the number of worm strains capable of stealing data, making it increasingly difficult to classify malware specimens into one category or another."

Downloader.MDW, a Trojan designed to drop other malware strains on the infected computer, was the most active malicious code in February, according to PandaLabs.
Bagle.RC took second place, and the Lineage.GXD worm, designed to affect users of the Lineage online game, was third.

The most active malware samples detected by PandaLabs in February:

1. Trojan Downloader.MDW
2. Worm Bagle.RC
3. Worm Lineage.GXD
4. Worm Bagle.RP
5. Worm Lineage.HJT
6. Worm Perlovga.A
7. Worm Bagle.HX
8. Worm Lineage.HIC
9. Worm Puce.E
10. Worm Lineage.HJB