You are mentioning two separate issues - your speed issue and the security issue claimed by the Which article.
If VM have identified a speed issue in your area then there is not too much you can do immediately on the speed problem until the area fault is cleared.
On the matter of the Which article claiming security problems, the article and its sources are somewhat light on detail as to what the perceived threats are. AIUI, the article was comparing old routers against the government's new 'Secure by Design' standards.
The main, and most obvious, issue in the case of the SH2 is changing the default administrative passwords which were all the same for all units when produced. The default wi-fi settings and passwords may also be weak compared to current standards but can be improved by the user changing them to something more current/secure.
The Which article mentions other vulnerabilities when a potential hacker was 'in the vicinity' of the router but doesn't elaborate on what that means. It might be the wireless issue mentioned above or may mean any hacker has to be connected to the user's network.
VM have denied any security issues with the older equipment. In the recent past VM have offered upgrades to SH2 users and below but I am not sure where that stands now as there have been mentions on the forum of Hub 3 units being in short supply. AIUI, VM have been recycling equipment which is still current for reuse, so you may get a 'new' hub that has previously been used by someone else
One of the forum team staff should be able to advise if you can currently get an upgrade or not to a newer VM hub.
