[exim] strange AUTHs in logs

Hi

I just read my logs and found something strange:

2005-07-31 09:34:19 ignoring AUTH=www000@??? from
H=www1.spektrum.de [194.175.173.101] (client not authenticated)

greping over my logs, I found more such entries. about 500, 250 of which
were from spektrum.de alone.
So, what does this mean?

The server sent
AUTH www000@???

and so corresponding
PASS ...

???

(Which would obviously make no sense, since there isn't such an account...)

Any guess anyone?

Regrads,
Steffen