Around 1400 new malicious codes were detected in July, increasing from the 950 discovered from the month previous, according to Trend Micro.
In a statement released last week, Trend Micro -- a company offering network anti-virus and security services -- highlighted the growing number of computer worms, viruses, Trojans and others, including the resurgence of the Bagle and MyDoom worms.
Three of the alerts in July were related to variants of Bagle, suggesting that the arrest of the Netsky author has cleared the way for the appearance of other worms. These variants accounted for over 700 of reported infections during the latter half of July.
A yellow alert was raised for a MyDoom variant on 26 July, which used social engineering to fool users into believing emails were either mail system error notifications or from friends.
Worryingly, Trend Micro also found an increasing prevalence of Trojan horses and backdoors, often used to attack one target or steal personal information, such as credit card numbers and system passwords.