I hate it when people try to vote against something that makes life easier, out of privacy concern and security...
If you have viruses on your machine, that's your own darn fault, why penalize everybody for your stupidity?
The second half has already been responded to, so I'll tackle this bit.
If you have malware on your machine, that's likely your own fault (most likely through ignorance). Unfortunately, everyone on your network, on your social network, and on the malware's distribution chain is penalized for your stupidity.
So let's back up one level...
Online voting makes life easier, agreed.
Unfortunately, abuse of online voting doesn't just affect the person not using it to vote, but also affects everyone in the municipality.
You can't have it both ways: either the upstream has to think of the privacy and security concerns, or the end operator (citizen) does.
As "online" implies global, it means that unlike mail-in, where abuse is likely limited to people who are actually a part of the municipality plus a few external interested parties, suddenly abuse is open to the entire world, where statistics indicate that a 0.001% of the 7 billion population = 70,000 actors likely to attempt to abuse the system for reason X instead of the 0.15 of a person who is likely to abuse the system for reason X locally.
The main way to ensure best security is to limit scope: only expose a function to the actors that need to access it. "On the Internet" does the inverse.
And that's just one reason it's a bad idea; there are plenty of others. All of them have solutions, but all the solutions are going to run afoul of statistics when you move a system that's been exposed to 15,000 people into an arena where it's exposed to 7 billion people.