Many well-known and heavily used web sites are using a fraud protection script that port scans your local computer for remote access programs. These ports are for legitimate reasons but are also known to be used for malicious purposes. Many of the sites using ThreatMetrix’s anti-fraud scripts are well known brands, including Citibank, TD Bank, Ameriprise, Chick-fil-A, Lendup, BeachBody, Equifax IQ connect, Sky, GumTree, and WePay port scanning our computers.
Source: https://www.bleepingcomputer.com/news/security/list-of-well-known-web-sites-that-port-scan-their-visitors/