Netsky-P, an email computer worm allegedly written by a German teenager, was the hardest-hitting virus of 2004, disrupting tens of thousands of businesses and homes worldwide, Web security firm Sophos says.
The worm accounted for almost a quarter of all virus incidents reported, Sophos said in a report on Wednesday, with four other Netsky variants also making it into the top 10, and the Sasser worm by the same writer taking third place.
"2004 was the year of the Netsky," Sophos senior technology consultant Graham Cluley said in a report covering the period December 2003 to November 2004, adding that Netsky-P was still the world's most widely reported virus, 8 months after its discovery.
Sasser, a worm which spreads not via email but via the Internet, attacking Windows computers not protected with a security patch from Microsoft, was first seen just two weeks after the patch was made available.
"The time period between patch availability and worm exploit is getting shorter than ever," Cluley said.
Overall, Sophos protected against more than 97,000 viruses, worms and Trojan Horses — which lurk inside a device without the user knowing it — during the year. More than 10,000 were new viruses.
All of the top 10 attacked Windows computers. "Motivated by the thought of spreading their malicious code as far and wide as possible, virus writers are likely to continue targeting the ubiqutious Microsoft and its users in 2005 and beyond."
Sophos said it had also discovered a new type of "phishing" attack in 2004 — in which fraudsters send out emails allegedly from real companies asking recipients for personal and financial information.
Instead of luring computer users to a fake Web site to steal their banking and credit-card details, the new wave of phishers use Trojan Horses to lie in wait for users to visit real banking Websites and then secretly record login processes.
The year's top hoax was a chain letter sent via Microsoft Hotmail, it said. Although hoaxes are not viral they clog up mail servers and confuse users.
During the year, a number of high-profile arrests were made including that of the 18-year-old German, who has confessed to the Sasser worm and is accused of creating Netsky.
An Australian email scammer who stole more than 2 million pounds ($3.9 million) was jailed, while Brazilian authorities made more than 50 arrests for Trojan phishing and the UK's National Hi-Tech Crime Unit made several arrests related to phishing, Sophos said.
But Sophos called for a formal framework to make it easier to report virus infections or unsolicited spam mail.
"Despite an increased number of arrests and convictions of spammers, the spam problem shows no sign of disappearing," it said.
"Those responsible for writing malware are more active than ever before."