Some spam can simply be an unwanted advertisement. under what circumstance can spam become a crime?

Spam become crime "when is causes serious damage to a computer or network".

The most widely recognized type of spam is email spam, however the term additionally applies to any message sent electronically that is spontaneous and mass. This incorporates: text spam, web index spam, blog spam, and so forth. A few people characterize spam considerably more for the most part as any spontaneous email.