Google is expanding seemingly by the minute, and acquisitions are playing a big role in the search engine leader’s quest to rule the technology world. Wednesday Google said it will buy a photo-sharing Web site called Panoramio and on Tuesday confirmed the acquisition of security software vendor GreenBorder Technologies. There are rumors Google will also purchase a provider of online RSS feeds called Feedburner for $100 million.

In all, Google has agreed to make at least 11 purchases of companies or technologies in the past year. Google usually doesn’t release financial terms of small deals, but the big ones are substantial: $1.65 billion for YouTube and $3.1 billion for DoubleClick (the latter deal is pending a federal investigation). A little bit more than a year ago, Google spent $1 billion for a 5% stake in AOL.

The past year’s purchases, which we describe below, have helped Google shore up gaps in its product line, develop a better office application suite capable of competing with Microsoft Office, and build on its massive success in online advertising. (Microsoft has made 13 acquisitions in the same time frame, including a $6 billion deal during May for aQuantive, a digital marketing and advertising company).

Pending acquisition:

April 2007: Google agrees to buy Internet advertising company DoubleClick for $3.1 billion. Microsoft, which failed in an attempt to buy DoubleClick, urged federal regulators to block the purchase, saying it would hurt competition in Web advertising. The Federal Trade Commission has just launched an antitrust investigation into the Google-DoubleClick deal.

Completed acquisitions:

May 30, 2007: Google agrees to buy Panoramio, a community photos Web site based in Spain that connects pictures to the exact geographical location where they were taken, allowing users to view those photographs in Google Earth. Google and Panoramio had already been working together for several months before the purchase, and the deal is expected to lead to further integration of Panoramio content with Google mapping technology.

May 29, 2007: Google buys GreenBorder Technologies, a maker of browser-based security software. The acquisition should help Google strengthen protection against malware across its line of Web applications. “The idea is that these guys have great expertise in the security domain that can provide obvious benefits to Google, its users and its advertisers,” a Google spokesman told InfoWorld.