To the best of my understanding it means that a system made by CGI for digital signing of documents (as in: you get something like a PDF from a government agency and need to digitally sign it and send it back) has had its source code and/or some data belonging to it leaked.

Skatteverket, the Swedish tax authority, has been quoted in media as confirming that they use CGI's system for digital document signing but that none of their data nor that of any citizens has been leaked.

https://www.svt.se/nyheter/inrikes/uppgift-statlig-it-inform...

"One of the government agencies that uses CGI’s services is the Swedish Tax Agency, which was notified of the incident by the company. However, according to the Swedish Tax Agency, its users have nothing to worry about.

“Neither our data nor our users’ data has been leaked. It is a service we use for e-signatures that has been affected, but there is no data from us or our users there,” says Peder Sjölander, IT Director at the Swedish Tax Agency."