What are the dangers of logging into websites using Tor?
A2AFacebook and etc are on https addresses now. Which mean there is another layer of encryption besides the 3 layers from tor. So the original, pure data is also encrypted. Which would prevent a simple, so called man-in-the-middle attack by the exit node. But there is report that government agencies (NSA) have successfully broken the "https" protocol. But I hope this doesn't deter you from using tor.Edit:The only "danger" from using tor is that your encrypted data might draw more interest since it's running on tor then normal data.
If ISP companies record each website their users visit, then don’t their databases become extremely big? How long do they keep this data?
What many people regard as a lot of data on their personal system, is not a lot for many companies.Let's continue with your 100 million rows example. Let's assume they track a few things about each visit: url, timestamp, ip-address, durations, maybe also browser and device information. Overall this maybe comes up to 30 columns in total.If you save this as a text file it might come to about 1–2 Gbyte. Compressed this will only be a few hundred megabytes. Even in a worst case scenario with 10 GB per day for one million user this would only come up to 3.6 terabyte peer year, which might take five 2Tb hard drives for redundancy, coming to less than $300 in storage cost - which is not a lot.This will likely be optimized further though. This kind of data is usually saved in a database which take up a lot less storage for data points like dates, durations, ip-addresses and the like. Compared to text files. Other string-type data (more storage) can also be converted to integer-labels with less storage (like browser info: chrome=1, Firefox=2, …). With more optimizations like these you can get 100M rows and 30 columns to about 200 Mb, which is negligible in today's IT world.So, saving this data for millions of customers might require a few dozen terabytes per year but thinking about the size of a typical ISP, this is not a lot of money.ISP will also usually save a lot of log-files for their infrastructure which often comes up to billions of rows per day. The storage cost for those is likely higher but overall storage is not that expensive anymore today.As for the storage duration it depends on where the ISP operates. Some countries with stricter privacy laws require the deletion after a few months, others might not require it at all.