There are two spiders from Yahoo! that you may have been noticing crawling over pages recently. The first, is named Yahoo! Slurp China has reportedly been around since mid-Novmember of last year. The second, is named Yahoo! Search Marketing Crawler and has just been discovered, I believe.
Yahoo! Slurp China found recent activity as reported at DigitalPoint Forums under the User Agent;
Mozilla/5.0 (compatible; Yahoo! Slurp China; Agent: Mozilla/5.0 (compatible; Yahoo! Slurp China; http://misc.yahoo.com.cn/help.html)
WebmasterWorld has an older thread on the topic that IP block is 202.160.178. and 202.160.179. and it resolves to *.inktomisearch.com. If you don't like this spider, the folks at WebmasterWorld say you can just block its user agent and it won't affect the main Yahoo! Slurp. They say block; "User-agent: slurp china"
Yahoo! Search Marketing Crawler is a fairly unknown spider that sprung up some recent concern at WebmasterWorld Forums. It has been reported from the IP address 188.8.131.52 and 184.108.40.206, which is resolving to Savvis and not Yahoo! Senior Member, StupidScript, says that this spider is an automated ad-checker. He also said that Yahoo! has never claimed ownership of this bot and that they blocked it only to stop "receiving mail from SBC-Yahoo subscribers." I am not 100% sure about this so I will do a follow up with Yahoo! Search Marketing on this crawler.