According to online sources, eBay.com uses a special script to scan visitors' PC ports in order to detect programs for remote access. Many of the scanned network ports are used by popular remote control tools such as Windows Remote Desktop, VNC, TeamViewer, and others.
Enthusiasts from Bleeping Computer conducted a study that confirmed that eBay.com really scans 14 different ports when a user enters an Internet site. This process is carried out using the check.js script and runs every time the resource is visited. The script performs a scan using a WebSocket to connect to 127.0.0.1 on the given port.
The source notes that port scanning is not carried out if the user is using a device running Linux when visiting the eBay site. However, when visiting the web platform from a Windows device, the scan is captured. It is assumed that such scanning is carried out to detect compromised computers that can be used by attackers to conduct fraudulent activities on the eBay site.
Recall that in 2016, reports appeared on the Internet that cybercriminals using TeamViewer were taking control of users' PCs to make fraudulent purchases on eBay. Since many eBay users use cookies to automatically log into the site, attackers could remotely control their computers and gain access to the platform to make purchases. Official representatives of eBay refrain from commenting on this issue.
Source: 3dnews.ru