They usually steal funds directly from mobile users' bank accounts, but sometimes their purpose is changed to steal other kinds of credentials.
The malware generally looks like a legitimate app, such as a banking application. When a victim tries to reach their genuine bank app, the attackers gain access to that too.
In Q1 2019, Kaspersky Lab detected around 30,000 modifications of various families of banking Trojans, trying to attack 312,235 unique users.
"The rapid rise of mobile financial malware is a troubling sign, especially since we see how criminals are perfecting their distribution mechanisms," Victor Chebyshev, a security researcher at Kaspersky Lab, said in a statement.
"For example, a recent tendency is to hide the banking Trojan in a dropper - the shell that is supposed to fly to the device under the security radar, releasing the malicious part only upon arrival," Chebyshev added.
A new version of the Asacub malware accounted for 58.4 per cent of all banking Trojans that attacked users, said the report.
Asacub first appeared in 2015. The attackers spent two years perfecting its distribution scheme and, as a result, the malware peaked in 2018, when it attacked 13,000 users a day.
Since then, its rate of spreading has closed down, although it remains a powerful threat - in Q1 2019, Kaspersky Lab detected Asacub targeting 8,200 users a day on average.
To reduce the risk of infection with banking Trojans, users should install applications only from trusted sources, ideally from the official app store, said the security researchers.
Kaspersky Lab said its solutions detected and repelled 843,096,461 malicious attacks from online resources located in 203 countries around the world.