It certainly seems to have been very active in Europe, and we think it's this one which has the side effect of picking up people's email addresses and sending you blank emails by hitting email servers.
We've had quite a few of these head our way over the last two weeks.
Here are the Kaspersky figures for April:
I-Worm.Klez 94.5 %
I-Worm.BadtransII 1.5 %
Win32.Elkern.c 0.6 %
I-Worm.Sircam 0.6 %
I-Worm.HappyTime 0.4 %
I-Worm.LoveLetter 0.3 %
I-Worm.Hybris 0.2 %
Win95.CIH 0.2 %
I-Worm.Cervivec 0.2 %
Trojan.PSW.Delf 0.1 %
Trojan.PSW.Gip 0.1 %
I-Worm.Magistr 0.1 %
Macro.Word97.Thus 0.1 %
I-Worm.Gibe 0.1 %
I-Worm.Nimda 0.1 %
I-Worm.Stator 0.1 %
JS.Trojan.Seeker 0.1 %
Backdoor.Death 0.1 %
IIS-Worm.CodeRed 0.1 %
Backdoor.Osirdoor 0.1 % ยต