Fraudulent app installations were up sharply in Q1 2018, according an AppsFlyer report, and shopping apps were particularly hard hit.

App installation fraud occurs when an installation is recorded and paid for, but no real user has actually downloaded the app.

Fraud is widespread across a variety of categories, but those that have a cost per install (CPI) tend to attract illicit activity, as each installation registers a higher payment. Meanwhile, apps in categories with broad reach are also vulnerable, thanks to the large potential audience.

That puts shopping apps, for which the CPI is 40% higher than the average, at high risk for installation fraud. AppsFlyer found that the cost of fraudulent shopping app installs reached $275 million in the first quarter of this year.

Aside from financial exposure, the study found shopping apps placed second in fraud rates: Three in 10 had a fraud rate of at least 10%, and more than one-fifth were exposed to at least 20% fraud. Some 17% of shopping apps had more than 30% fraudulent activity.

Shopping apps' overall fraud rate was 35% higher in Q1 2018 compared with the final quarter of 2017. Additionally, they had the highest number of fake installs due to bot and hijacking attacks, and of installs rejected due to behavioral anomalies. 

eMarketer forecasts that 215.9 million US smartphone users will install an app on their devices this year. That works out to 94.2% of all smartphone users.