About 2% of emails were attacked with a Zbot/ZeuS spyware programme.
Almost three quarters of email traffic during July was spam, according to a report from the Kaspersky Lab.
About 71% of the email traffic during July was spam, while 2% of emails were attacked with a Zbot/ZeuS spyware programme.
The Zbot/ZeuS spyware programme is said to be targeted at online banking service users, who have logged in using a Windows system or an Android mobile device.
A new threat named SMS-Flooder.AndroidOS.Didat. entered into the list of top 20 email threats in July, targeting mobile Android operating systems.
Kaspersky Lab Content Analysis Department head Darya Gudkova said: "The appearance of this new threat in the Top 20 spam ratings confirms our expectations – the steady growth of Android users will inevitably lead to an increase in the number and variety of these types of threats.
"These programmes capable of sending out text messages will no doubt soon be joined by Trojans that steal confidential data."
The report also revealed that the attackers used fake emails seeded with the Zbot Trojan, similar to official notification from banks, online stores, social networks, or popular delivery services during the month.
China was responsible for 23.4% of the malware, followed by the US with 18% and South Korea with 14.9% of the total spam.