May 7, 2003 - Symantec Security Response released its monthly listings of the top viruses and vulnerabilities reported in April 2003. The table below represents the most prevalent viruses for March and April 2003.
| April 2003 | March 2003 |
| W32.Klez.H@mm | W32.Klez.H@mm |
| W95.Hybris.worm | Backdoor.Dvldr |
| W32.HLLP.Handy | HTML.Redlof.A |
| Backdoor.Sdbot | W95.Hybris.worm |
| W32.Kwbot.C.Worm | W95.Spaces.1445 |
| W32.Pinfi | W32.FunLove.4099 |
| W32.Bugbear@mm | W32.Nimda.E@mm |
| W32.Gibe.B@mm | W32.HLLW.Deloder |
| W32.Sobig.A@mm | W32.Bugbear@mm |
| W32.Opaserv.Worm | W32.HLLP.Handy |
Symantec also identified the top five vulnerabilities as: