###### Abstract  
During the recent COVID-19 pandemic, people were forced to stay at home to protect their own and others' lives. As a result, remote technology is being considered more in all aspects of life. One important example of this is online reviews, where the number of reviews increased promptly in the last two years according to Statista and Rize reports. People started to depend more on these reviews as a result of the mandatory physical distance employed in all countries. With no one speaking to about products and services feedback. Reading and posting online reviews becomes an important part of discussion and decision-making, especially for individuals and organizations. However, the growth of online reviews usage also provoked an increase in spam reviews. Spam reviews can be identified as fraud, malicious and fake reviews written for the purpose of profit or publicity. A number of spam detection methods have been proposed to solve this problem. As part of this study, we outline the concepts and detection methods of spam reviews, along with their implications in the environment of online reviews. The study addresses all the spam reviews detection studies for the years 2020 and 2021. In other words, we analyze and examine all works presented during the COVID-19 situation. Then, highlight the differences between the works before and after the pandemic in terms of reviews behavior and research findings. Furthermore, nine different detection approaches have been classified in order to investigate their specific advantages, limitations, and ways to improve their performance. Additionally, a literature analysis, discussion, and future directions were also presented. online reviews; spam reviews; detection; COVID-19; survey +
Footnote †: journal: Medical Informatics  
regarding the quality of the internal keyboard. In order to meet consumers' expectations, the manufacturer can consider these reviews and adjust the keystrokes. Thus, positive reviews can cause major financial gains, while negative reviews may even lead to sales loss [9]. As a result, more merchants are now taking into account the general public's opinions for the products' decision making [10; 11; 12]. For example, in 2004, one consumer wrote a review about the U-shaped Kryptonite lock and how it can easily be opened using a ballpoint pen [13]. This hustle caused by this review forced the company to replace any affected lock without any charge. The Kryptonite incident attests to the importance of online reviews. Furthermore, due to the detrimental situation (COVID-19 quarantine), reading and posting reviews across all platforms have increased rapidly [14]. Unfortunately, the rise affected not only legitimate reviews but also spam reviews. Spam reviews are reviews characterized as fraud, fake, malicious, and false opinions intended for publicity or profit. Due to this attitude, most consumers and organizations would be misled away from making the correct decisions [15]. As a result of spam reviews, it became harder to improve products and services because of the failure to recognize feedback and reviews from real customers. This kind of review can be easily posted without any constraint on several platforms, so certain product providers or vendors could abuse this to promote their products and services or to disparage their competitors. Media news, such as BBC and New York Times, reported that there are more spam reviews on websites than real ones, for example, a photography company revealed to have posted thousands of spam reviews [16]. Accordingly, detecting spam reviews is a requisite nowadays, since without solving this issue, consumers will stop trusting completely online review platforms [17]. To counter this issue, industry and academia expand their efforts to identify spam reviews in all possible ways.