SPLK has a market cap of $3.5 billion, and IBM would need to pay $5 billion to acquire them. I do not think IBM will spend $5 billion on a firm that is currently generating LESS than $200 million in revenues.
I believe you're missing the point regarding revenues. The scale and branding SPLK has with big data and now website security is something IBM can really use. When you get a chance, look at SPLK's customer base and revenue growth over the past 2 years.
SPLK is certainly trading like they're on someone's radar screen, it could be IBM, or ORCL, or even MSFT.