Trojan.Adclicker

Trojan.Adclicker is a detection name used by Symantec to identify malicious programs that share the primary functionality of artificially generating traffic to pay-per-click Web advertising campaigns in order to create or boost revenue.


Background information
When making use of Web-based advertising campaigns, advertisers typically pay advertisement publishers each time a user clicks on one of their advertisements. A typical sequence of events is:

1. An advertiser creates an advertisement and sends it to a publisher
   
2. A publisher publishes the advertisement so that it is displayed to users
   
3. Users click on the advertisement and are redirected to the advertiser's website
4. The advertiser pays a fee to the publisher for each of the users' clicks
   

If a criminal group or their affiliates pose as a publisher, they can generate revenue from the advertiser(s) by artificially generating fake 'clicks'. One way in which this may be achieved is through the use of a Trojan horse program that runs on unsuspecting users' computers.


Advertising networks
The above sequence is complicated by the existence of Web advertising networks that act as a middleman between the advertiser and the publisher; these days, most Web advertising campaigns are conducted with the aid of such a network. The networks typically allow advertisers to select and bid for certain keywords to be associated with their advertisements, with the advertising networks being able to display appropriate advertisements to users, often based on their browsing habits. The above sequence of events in this case should be:

1. An advertiser creates an advertisement, selects certain keywords, and sends them to an advertising network
2. The advertising network places the advertisement on certain publishers' websites and on pages that are likely to be of interest to the user
3. Users click on the advertisement and are redirected to the advertiser's website
4. The advertiser pays a fee to the advertising network for each of the users' clicks
5. The advertising network pays a portion of those fees to the publisher

The same Trojan may be used whether or not an advertising network is in place; assuming that the pay-per-click fraud goes undetected, the advertising network must still pay the 'publisher', which in this case is the criminal group. The fraudsters therefore still profit from the scam.

Note that in some cases, the advertising network and the publisher may be the same entity.


How does the Trojan 'click' on the advertisements?
The primary functionality of this family of Trojans is to generate fake 'clicks' on Web advertisements by sending HTTP GET requests to predetermined URLs. These requests are the same as those that may be sent by a Web browser when a legitimate user is browsing the Web. The Trojan may also falsify the 'referrer' field in the HTTP request in order to mask the fake nature of the access.


Other functionality
Some programs detected as Trojan.Adclicker may be designed to perform other actions. Criminals may produce programs to 'click' on their competitors' advertisements, thus costing them money. Alternatively, personal or political factors may be involved. The programs may also be used to generate revenue though referrer fees by creating fake 'clicks' on certain websites or advertising campaigns.


What happens after the Trojan is installed?
Programs detected as Trojan.Adclicker typically copy themselves to a system folder in an attempt to remain inconspicuous, and create a load point so that they run every time Windows starts. The Trojans may also perform the following actions:

• Lower security settings
• Attempt to download files, including other malware
  
• Display messages and/or advertisements

The Trojans typically then begin their routines to generate fake clicks.


Are there any tell tale signs?
In general, programs detected as Trojan.Adclicker aim to execute without the knowledge of the user, but indicators of infection may include slow or jittery Internet browsing. In some cases the Trojans may consume significant bandwidth. Some variants of Trojan.Adclicker may additionally display messages and/or advertisements on the compromised computer.


What are the risks?
The most immediate risk to the user is that of Internet use being disrupted. This may be a direct result of the bandwidth being consumed by the threats, or in extreme cases users may find that their ISP throttles their connection or disconnects it altogether. Alternatively, users may find that they are charged extra by their ISP once they have consumed more than an allotted monthly bandwidth cap.

Users may be vulnerable to the effects of other malware that may be downloaded by the threats.


What can I do to minimize the risks?
As a general rule, users should always run up-to-date antivirus software with real-time protection such as Norton Antivirus, Norton Internet Security, Norton 360 or Symantec Endpoint Protection. In addition, a firewall -- or better still, an Intrusion Prevention System (IPS) -- may help to block back channel activities initiated by these types of malicious programs. Program controls such as those found in Symantec Endpoint Protection can also help to prevent unknown programs such as these from executing in the first place.


How can I find out more?
Advanced users can submit a sample to Threat Expert to obtain a detailed report of the system and file system changes caused by a threat.