A computer worm is a type of Trojan that is capable of propagating or replicating itself from one system to another. It can do this in a number of ways. Unlike viruses, worms don’t need a host file to latch onto. After arriving and executing on a target system, it can do a number of malicious tasks, such as dropping other malware, copying itself onto devices physically attached to the affected system, deleting files, and consuming bandwidth.
Downloaders and droppers are helper programs for various types of malware such as Trojans and rootkits. Usually they are implemented as scripts (VB, batch) or small applications.
They don’t carry any malicious activities by themselves, but just open a way for attack by downloading/decompressing and installing the core malicious modules. To avoid detection, a dropper may also create noise around the malicious module by downloading/decompressing some harmless files.
Very often, they auto-delete themselves after the goal has been achieved.
Trojan is a malware that uses simple social engineering tricks in order to tempt users into running it. It may pretend to be another, legitimate software (spoofing products by using the same icons and names). It may also come bundled with a cracked application or even within a freeware.
Once it is installed on the computer, it performs malicious actions such as backdooring a computer, spying on its user, and doing various types of damage.
Trojans are not likely to spread automatically. They usually stay at the infected host only.
Toolbars are software extensions that are visible in the GUI of the host program. In the case of PUPs, the host program is usually a browser. The visible part of the toolbar can vary from one extra button added to the browsers own taskbar, to the bar over the full width at the top of the browser window.
Sweet Orange is a type of exploit kit, or in other words, malicious code found on compromised websites with the intention to find vulnerabilities on a computer by which said computer can be infected. In addition to compromised websites, they also operate deliberate traps that users get redirected to. Sweet Orange also uses malvertising, where malicious advertisements are placed on legitimate websites.