International revenue share fraud (IRSF), also known as toll fraud, is a type of fraud where fraudsters artificially generate a high volume of international calls/SMS on expensive routes. Here’s how it works. Fraudsters exploit Okta’s authentication flow and make expensive phone calls and/or texts as part of the MFA flow where phone/text is used as one of the factors Fraudsters tend to make calls to what are known as premium rate numbers or other high-cost destinations to maximize the profit Fraudsters take a cut of the revenue generated from these calls Due to the high costs associated with long-range international telephony transactions, toll fraud can bear a significant financial impact on the business. However, for many of our customers, SMS and voice are part of a crucial MFA flow that must remain reliable and uninterrupted. In this article, we will share how we protect our systems from toll fraud.