During latest days of November 2017 Monero difficulty, according to this chart, was around 30G and now is around 80G.
What happened to it?
And what should we expect for the near future?
It means that the network is used by more powerful miners. Difficulty adjusts to the network hashrate (after every block, unlike Bitcoin which adjusts difficulty only every 2016 blocks, around two weeks for 1 block / 10 minutes), meaning it will be more difficult to mine a block the more miners will join the network (if the overall hashrate goes up).
I expect the hashrate to rise over time, as I believe Monero to be more profitable to mine in the future. The more profitabel Monero will be to mine in the future, the more miners will join, causing the hashrate and difficulty to rise. This is so new blocks are still mined roughly every 2 minutes, even if computational power increases.
The reason for the increase lately could be (but doesn't have to be) because of a botnet mining Monero. But that alone wouldn't increase difficulty so much.
This is not financial advice and only reflects my own opinions.
ASIC producers created Cryptonight asics secretly. And they sold them to miners with astronomical prices but now they hit the dust thanks to the algorthm changes.