I would dearly love to see people boycott Yahoo until they either change their attitude to fraud or are driven to the wall and closed down.
About a year back I started receiving a large number of the
"Nigerian Scam" emails. The kind where the writer has $16Million trapped in a bank account and they have picked you out of all the people in the world to help them "liberate" the money for a hefty percentage of course. And as far fetched as these stories are, enough people do get actually get caught to make it profitable enough for the thieves to continue running these scams.
As a result, instead of just filtering and deleting these emails I thought that I would at least try and do my bit to put the thieves out of business by forwarding the emails to the abuse department of the various email service providers.
For the first few months most of the free email providers were evenly represented, hotmail, gmail, aol, live, yahoo, etc. on forwarding the emails to the abuse department I would receive an automated reply saying that they would look into the matter and take any necessary action. Invariably a test email the following day to the relevant email address would be returned "address unknown" confirming that the email account was closed.
The only odd one out is Yahoo. Instead of taking action Yahoo sends an automated email response directing one to a web page which explains how a Yahoo account holder can report received spam. There appears to be no mechanism for non-Yahoo account holders to be able to report emails received from a Yahoo account

So it doesn't really surprise me that Yahoo is particularly vulnerable to that sort of thing, they really don't seem to take user security too seriously.
I still get a few fraudulent emails on a daily basis, but now 100% of these emails have a Yahoo return address because Yahoo is the only email provider that condones fraud.
Boycott Yahoo! 