Comment by xorcist

Network switches typically aren't known for their outstanding security record, but the vlan tags themselves are trivial and should be hard to mess up. Should someone hack your switch all bets are off, but as long as you don't have management accessible in-band you should be fine. Security problems are more likely to stem from bad configuration.

> Can't a device on VLAN1 not peek at VLAN2 traffic if it sits on physical connection where packets from both VLANs happen to travel?

That would be an exceptionally weird configuration. If a device "sits on VLAN1" that typically means that it's on an "untagged" port where only VLAN1 traffic is allowed. Ports that carry multiple VLANs are "tagged" ports and you normally wouldn't say they "sit" on any specific VLAN, precisely because that port carries tagged traffic for multiple VLANs. It's at best an irregular use of the terminology but likely a misunderstanding somewhere.