According to statistics from Kaspersky Lab, adware programs and Java-based downloaders were the most common threats encountered on the Web during December.
There are three separate adware components that made it to Kaspersky's top 20 Internet malware list for last month.
The most frequently encountered one was AdWare.Win32.HotBar.dh which tried to infect a number of 203,975 distinct users.
It includes HotBar, Zango and ClickPotato and was the most prominent threat overall, including all categories.
The other two adware samples, AdWare.Win32.FunWeb.di and AdWare.Win32.FunWeb.fq, scored lower with 70,088 and 36,187 unique instances.
The second most common threat on the Web last month, with 140,009 detections, was Trojan-Downloader.Java.OpenConnection.cf, a dropper which uses the OpenConnection method of an URL class to download malware on the computer.
Another variant detected as Trojan-Downloader.Java.OpenConnection.bu came in seventh place in the top with 70,006 instances. At one point during a 24-hour period last month, these Java-based downloaders triggered as much as 40,000 detections.
Detections for exploits targeting flaws in Java, Adobe Reader and Windows itself entered the top fifteen, while scareware scripts also made their presence felt.
"The tactics used by the cybercriminals remained the same. Surfing the web is still a dangerous pastime, while social engineering is routinely used to entice users into opening malicious links or downloading malicious or fraudulent programs
Vyacheslav Zakorzhevsky, a security expert at Kaspersky Lab.
However, he noted that last month was the first time when malicious PDF documents that use Adobe XML Forms were spread en masse.