Microsoft is thinking about buying Salesforce and its stock is skyrocketing again

Microsoft is thinking about making a play to buy Salesforce now that the company has been approached by someone else about a possible acquisition, sources have told Bloomberg.

This is kicking the tires and a deal is not in the works, though, those sources said.

Still, executives at Microsoft have sort of been preparing for the day when they might get a chance to compete for Salesforce, these sources told Bloomberg.

Salesforce reportedly hired two investment banks to help it respond to offers. Such responses could include turning down buyers, or going all-out and opening itself up for a sale from multiple bidders.

Salesforce's stock is already soaring on this news. It had a market of $47 billion, up to nearly $49 billion.

It's unclear who the original takeover offers are coming from, but if the deal goes through it would be the largest software company to get acquired in history.

Speculation was that the original take-over talks were coming from major rivals Oracle and/or Microsoft. Oracle CEO Safra Catz declined to comment on that during a press conference last week, but others close to the company did not think Oracle was the one making this play. Another potential player, SAP, has said it is not the one either.

Microsoft and Salesforce used to be bitter rivals, but last year they struck a partnership to make their software work better together. And both the CEOs of both companies have been publicly praising each other.

Microsoft, which sells its own customer-management software, is not big in that market as Salesforce. Last week, the company vowed to reach a $20 billion revenue run rate for its commercial cloud business by its fiscal year ending June 30, 2018.

More to come.