Scareware

Scareware is a form of malicious software that uses social engineering to cause shock, anxiety, or the perception of a threat in order to manipulate users into buying unwanted software. Scareware is part of a class of malicious software that includes rogue security software, ransomware and other scam software with their computer, then suggesting that they download and pay for fake antivirus software to remove it. Usually the virus is fictional and the software is non-functional or malware itself. According to the Anti-Phishing Working Group, the number of scareware packages in circulation rose from 2,850 to 9,287 in the second half of 2008. In the first half of 2009, the APWG identified a 585% increase in scareware programs.

The "scareware" label can also apply to any application or virus which pranks users with intent to cause anxiety or panic.

Internet security writers use the term "scareware" to describe software products that produce frivolous and alarming warnings or threat notices, most typically for fictitious or useless commercial firewall and registry cleaner software. This class of program tries to increase its perceived value by bombarding the user with constant warning messages that do not increase its effectiveness in any way. Software is packaged with a look and feel that mimics legitimate security software in order to deceive consumers.

Some websites display pop-up advertisement windows or banners with text such as: "Your computer may be infected with harmful spyware programs. Immediate removal may be required. To scan, click 'Yes' below." These websites can go as far as saying that a user's job, career, or marriage would be at risk. Products using advertisements such as these are often considered scareware. Serious scareware applications qualify as rogue software.

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Wikipedia