Enlarge (credit: Getty Images)

Security personnel at Microsoft are seeing a big increase in the use of Web shells, the light-weight programs that hackers install so they can burrow further into compromised websites.

The average number of Web shells installed from August, 2020 to January of this year was 144,000, almost twice that for the same months in 2019 and 2020. The spike represents an acceleration in growth that the same Microsoft researchers saw throughout last year.

(credit: Microsoft)

A Swiss Army knife for hackers

The growth is a sign of just how useful and hard to detect these simple programs can be. A Web shell is an interface that allows hackers to execute standard commands on Web servers once the servers have been compromised. Web shells are built using Web-based programming languages such as PHP, JSP, or ASP. The command interfaces work much the way browsers do.