April 30, 2005 - Mytob-Z was discovered in April and was the only new virus to make the top ten even though there were fewer reports on this virus in comparison to others.

Sophos on Friday published its monthly report that highlights the top ten viruses causing problems for businesses around the world.

The report revealed that Zafi-D, which first appeared at the end of 2004, continued its reign at the top of the list for the fifth month running, accounting for 46.6 percent of all viral alerts.

Only one new threat -- Mytob-Z -- managed to break into the chart for April, appearing in seventh place.

"During the month of April, several older viruses maintained their spot on the chart," said Gregg Mastoras, senior security analyst at Sophos.

"The Zafi family of viruses accounted for more than 50 percent of all the viruses reported to Sophos this month," he said.

It could be that many of these worms were able to spread in multiple languages, therefore catching some users off guard, he explained.

"Users should always be suspicious of unsolicited e-mail in any language and they must ensure that they keep their virus protection up to date," said Mastoras.

Mytob-Z was discovered in April and was the only new virus to make the top ten even though there were fewer reports on this virus in comparison to others.

"Mytob-Z, which spreads quickly, drops a backdoor Trojan horse that can be used by remote hackers to gain access and control over a victim's computer," said Mastoras. "The computer can then be spied on or used to send spam or launch denial of service attacks."