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I'm trying to form this question in a way that's suitable for this particular SE site.

I have a MacBook, that was given to me for use on a professional basis. It worked perfectly.

My rather older personal computer later had a hard-drive failure, so I downloaded the Torrent client Transmission and used the Macbook to download an old Katherine Hepburn movie, On Golden Pond, and good old Caddyshack.

Within a week, the Mac had slowed to the point of utter unusability, and I had to reinstall the operating system to restore it to a working state. I'm still wondering what caused the problem. Torrenting had never given me any troubles in the past, never once. I've never had my computer slow down that way, but then again, I've also never used a Mac.

Without making comments on the morality of torrenting, which is off-topic, or the semi-questionable decision to use a work laptop for the above purpose, can anyone say with any certainty whether there might be a link between my use of Transmission and the resultant failure of the computer? I am aware of the dangers of torrenting, but I had never seen any manifest before.

I can say absolutely that no other changes took place on the computer during the relevant timeframe. No other programs were downloaded, no popups clicked, no suspicious email links clicked. Which is what leads me to wonder about Transmission.

share|improve this question
Have you tried installing Transmission again to see if you get the same thing? – imtheman Jul 20 '12 at 18:28
I'm terrified to try that. Having to reinstall the OS made for a lot of lost time in reconfiguring my various development environments. – Aerovistae Jul 20 '12 at 19:39
Oh, I thought maybe you just reinstalled the OS, so it was clean, but since that's not the case then yeah you probably don't want to do that... – imtheman Jul 20 '12 at 19:41
up vote 3 down vote accepted

I've seen torrent clients drastically slow down networking while the torrent clients are running (because they're using so much bandwidth and because of the overhead of opening/closing peer connections all the time). But otherwise, no, if you weren't leaving Transmission running all the time, Transmission probably didn't cause the problem.

Next time run Activity Monitor or top -o cpu to see what's eating CPU time.

I've seen Spotlight (technically, the related mds and mdworker processes) use a lot of CPU time and cause slowness while perpetually trying to rebuild a corrupted Spotlight index. I cleared it up by stopping Spotlight, deleting the index completely, using Disk Utility to fix any filesystem corruption, and then starting up Spotlight again.

If you can't find anything hogging the CPU, then you might have a filesystem corruption problem or disk malfunction that's causing slow disk access.

First, run a Disk Utility "Verify Disk" or "Repair Disk" to look for (and correct) filesystem corruption.

If that doesn't help, run the third party SMART Utility app to see if your disk has any pending, reallocated, or remapped sectors. If your hard drive has a failing sector that is pending remapping but has not been remapped yet, then any time anything needs to access that sector, it'll take a long time to time out, and the system hangs with a spinning pinwheel for several seconds whenever that sector gets read. Writing to that sector is how to let the drive remap it, but there are some kinds of filesystem structures that get read a lot but almost never get written.

Reinstalling the OS would have caused many GibiBytes of your disk to be rewritten, which would have a high likelihood of causing any bad sectors to get remapped.

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Very useful advice. Will refer back to the next time I have such a problem. – Aerovistae Jul 20 '12 at 19:44

I know it's quite rare for macs to get a virus, but it sure sounds like you got one. That's one of the main things you need to watch out for when downloading torrents. Though it's really impossible to say for sure. I guess just be more careful when downloading torrents.

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It's really so exceedingly rare that it's really not worth mentioning. The Flashback trojan (not virus) from earlier this year is really the only significant malware attack that OS X has ever seen in its 12-year lifetime, it didn't cause slowness, and a later automatic software update from Apple has eradicated it. I don't mean to sound smug, and I really don't think Macs are inherently more secure than Windows PCs, it's just that the reality is that Macs have been lucky so far and there really aren't any Mac viruses worth worrying about. – Spiff Jul 20 '12 at 19:11
Right, macs aren't any more secure than windows, it's just so few people use them (in comparison to windows) that it's not worth the time to make a virus for them. – imtheman Jul 20 '12 at 19:15
@spiff I'm really inclined to say you're right, because that makes sense, and I'm glad, because if Peter's case were true I would feel rather guilty about having recklessly demolished my own productivity this week. It's good to know that is apparently not the case. – Aerovistae Jul 20 '12 at 19:44

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