ZDNet India : Yahoo to Trillian: Talk to the hand:
"Yahoo said it will continue changing its protocols to prevent clients such as Trillian from finding new ways to incorporate Yahoo. Again, the measure was cited by Yahoo as a way to prevent IM spam.

'By making frequent protocol changes, it is our expectation that spammers will be blocked from abusing our system to spam our users,' Osako said.

IM spam, commonly referred to as 'spim,' has been flagged by experts as a growing problem. However, experts have also written off spim as a far cry from e-mail spam, which has caused enormous headaches for consumers and businesses alike. "