In PuTTY, left-click and drag normally selects and copies the entire line content. However, you can change this behaviour to block select like in a MS DOS window.

To make a block select in PuTTY, click and hold “ALT” and then left-click and drag on your mouse. This will make block selection.

If you want to make this the default behaviour,

1. Load a saved session or load “Default Settings”.
2. In the left pane, click Window – Selection.
3. In the right pane, select “Rectangular Block” under Default Selection mode.
4. Click Sessions and save the loaded session.
5. Repeat the above for every saved session.