The ransomware and botnet attacks that have been dominating the headlines lately are only two of the online threats that organizations have to deal with these days.

An equally pressing danger is the rise of so-called account takeover campaigns that target users with privileged access rights to a service or personal data in their profiles. According to an April report from Verizon Communications Inc., such attacks represent the single biggest threat to web services today. Castle Intelligence Inc., a San Francisco-based security startup that raised $2 million in funding today, hopes to make those attacks more manageable.

The investment was led by First Round Capital and included additional contributions from F-Prime Capital, FundersClub plus several unnamed angel investors. Castle will use the cash to expand the capabilities of its namesake security service, which employs machine learning technology to identify signs of account theft. Its algorithms implement a similar detection approach as the artificial intelligence-powered endpoint protection software that Israel’s Fortscale Ltd. has developed to help companies spot suspicious activity behind the firewall.

After a user signs up for a web service or mobile app protected by Castle, the service starts tracking key metrics such as the location from which they logged in, when they’re most active and what pages they frequent. Its algorithms crunch the data to create a behavioral model that serves as a sort of yardstick for assessing account activity. From there, every important action is checked against the model to find anomalous patterns that may point to a breach.

Castle can automatically suspend an account after finding signs of compromise — say, a login from an unknown device in a foreign country — and provides the option of sending a security notification to the associated email address. It does so without requiring organizations to make any major modifications to their services. Embedding the tool in a website is about as straightforward as setting up Google Analytics, while mobile apps are able to tap its capabilities via a relatively simple application programming interface.

Castle claims that its service has blocked over 250,000 account takeover attempts to date across hundreds of sites. The startup will use today’s investment to attract more customers and build its offering into a “complete account security suite for companies of all sizes,” which presumably means that it’s planning to add more enterprise features such as integration with third-party security tools.

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