Recently there has been a growing problem of for-profit conferences which do not follow standard (or in some cases, any) scientific peer review.
Publishing at these conferences can be bad for both research and career progression. Hallmarks of these conferences include overly-general
calls for papers and obscure programme committees.
A related problem is the appearance of fake conference ratings web sites, which achieve a veneer of scrutability by listing well-known
conferences alongside fake conferences.
Fortunately, reputable conference rankings can be found at
Microsoft Research Asia,
and (slightly dated) CiteSeer.