Portal is silent intrusion program emulates a part of the data wall and integrates itself into it (3 turns, no alert). Once this is done, it opens a portal in the data wall and allows the Netrunner to slip through. When the Netrunner has passed through. the program will end its run and the data wall will return to normal (unlike other Intrusion programs. there is no giveaway gap left behind in the Data wall).
Source[]
- Rache Bartmoss Guide to the Net, pg.148