The infamous Klez worm has retained the top spot in security firm Sophos PLC's most frequently occurring viruses table for the 15th month in a row, while 475 new viruses were discovered in April.
Two old favorites also reared their heads again -- Lovegate-E and Funlove -- spreading concern that individuals and companies are not keeping their antivirus software and firewalls up to date.
"It's no good installing the software if it's not maintained," said a company spokesman.
A new virus Datemake Dialler also made its way into the top 10. The malware, known as a Dialler, is programmed to dial a premium rate telephone line, typically with the intent of gaining access to adult material.
"Businesses should apply strict computing guidelines to avoid getting stung by a huge telephone bill and embarrassed by these seedy programs," said Graham Cluley, senior technology consultant at Sophos.
Top viruses were:
1. W32/Klez-H, 12.7 percent of complaints
2. W32/Lovgate-E, 4.9 percent
3. W32/Bugbear-A, 4.3 percent
4. W32/Sobig-A, 3.3 percent
5. W32/ElKern-C, 2.9 percent
5. W32/Yaha-E, 2.9 percent
5. W32/Yaha-K, 2.9 percent
8. JS/NoClose, 2.1 percent
9. W32/Flcss, 1.9 percent
10. Dial/Datemake-A, 1.6 percent